In this rapidly changing environment of human beings, the parents and educators as a whole recognize the significance of developing the inherited qualities of their children to make them self-sufficient, independent and creative learners, consequently, they will be enbled to meet their diversified demands and goals for their all-round development. The purpose of the schooling of children is to educate them to the best of their abilities in a congenial environment, whereas the teachers deal with them by studying their psychological constructs, and the responsibilities of the teacher become the facilitation of positive growth (Rooyen, 1997). In this 21st century, the focus is on the harmonious progressive development of the child through a child-centered approach, where the learners are given the utmost freedom in the teaching-learning process. The behaviouristic approach of teaching is now replaced with a constructivist approach, where the learners get the freedom to construct their knowledge through their previous knowledge. Still, it can be said that education is still focused on teaching of basic skills such as reading, writing, and arithmetic, presenting a confined curriculum. But, in this accelerating information and communication age the children need such skills which will help them to control their lives and their learning (Rooyen, 1997). They need more and more knowledge and skills, but more importantly, they need the capacity to gather new knowledge from their own experience. In this present situation, the emphasis is more on the cognitive domain of knowledge and also on the psychomotor domain of knowledge, but to some extent, the affective domain of knowledge is being neglected. So, in the present education system thinking is given less importance, which becomes a hurdle for the children to know about their potentialities and inherited abilities. Therefore, the concept of 'Metacognition' plays a vital role in this perspective, where the primary focus is given on the thinking of the students, rather than other things. Metacognition plays a vital role both in teaching and learning, as in both these cases thinking occupies the most important role.

In this present paper, an attempt is made to analyze the researches on metacognitive strategies and interventions used in teaching, and highlight the important metacognitive strategies to improve the teaching-learning process.

The monitoring of all kinds of cognitive activities occurs through human actions with some basic elements like metacognitive knowledge, metacognitive experience, goals and actions. Metacognition plays an important role in regulating and monitoring the thinking of individuals. Flavell is considered as the father of metacognition, as for the first time the concept of metacognition was used by him. According to him, metacognition refers to the cognitive process and product of an individual's knowledge. The concept of metacognition is reflected abstraction from the school of developmental psychology of Jean Piaget, and also it is the transference from regulation to self-regulation inspired by Vygotsky's theory of development. In his original research of Flavell, he has defined metacognition as knowledge and cognition about cognitive objects. He also subdivided the metacognitive knowledge into three categories as follows: knowledge of the person, task and strategy variables.

Figure 1 shows the components of metacognitive knowledge, which refer to the perspectives of an individual's abilities. It also indicates the knowledge of individuals that is stored through their cognitive activities, tasks, goals, and experience too. 'This metacognitive knowledge consists of three basic variables, according to Flavell, such as person variables, task variables and strategy variables. The person variables include the knowledge of an individual's knowledge, which is intraknowledge; it also includes the knowledge of individuals about the knowledge of others' groups, which is interknowledge. Finally, it also includes the general knowledge that most people acquire through their cognition, which is universal knowledge. The task variable includes the knowledge of individuals gathered through their experience; it involves different kinds of informationprocessing demands that individuals need to perform multiple tasks. The strategy variable includes the dynamic cognitive strategies or procedures of the individuals that they apply to accomplish their goals ( Flavell, 1979).

Figure 1. Components of Metacognitive Knowledge by Flavell

Flavell distinguished the concept of cognition and metacognition with a suitable example. Metacognition experience mainly activates different interventions and strategies to accomplish two types of goals i.e., cognitive and metacognitive. For example, occasionally the students do not know certain chapters well enough in their text to pass the nearby exam, so they read the chapter thoroughly once again (cognitive strategy), which simply improves their knowledge about the chapter they did not know earlier. After that, the students understand that they have improved their knowledge about the chapter to pass the exam, then they try to ask themselves different questions that how well they can answer them (metacognitive strategies), which aims at assessing the gathered knowledge of the students and generating new metacognitive experiences. So, it can be said that cognitive strategies are meant for performing different cognitive functions among individuals; on the other hand, the metacognitive strategies are meant to monitor purposes.

Metacognition refers to the abilities of an individual to apply the previously gained knowledge and experience, to plan a framework for operating learning tasks, to follow strategies in solving problems, to make reflection and evaluation with necessary modifications. Metacognition involves the awareness of individuals' knowledge of what they know and do not know. The cognitive strategies the students use are nothing but their basic mental abilities which involve thinking, studying, learning, recalling, memorizing, analyzing, associating or comparing concepts or objects which are helpful for individuals to accomplish a particular goal.

Figure 2 describes the concept of metacognition and its components in an easier way:

Figure 2. Components of Metacognition

Knowledge about Cognition: According to Flavell, knowledge about cognition is the individual's knowledge about their cognitive functioning, which includes Declarative, Procedural and Conditional knowledge'. The factual knowledge that the student needs before being able to implement or process their critical thinking related to the topic is called declarative knowledge, which also includes students' knowledge and experience about their skills, intellectual resources and abilities. Presentation, demonstration and discussion are the sources of getting declarative knowledge. The application of the knowledge of the students to complete a procedure or process is termed as procedural knowledge, which helps the students to know about the process and apply the process in various situations. Usually, knowledge obtained through discovery, cooperative learning and problem-solving is the source of procedural knowledge. Conditional knowledge refers to situations under which the procedures or skills to be transmitted, usually, the information obtained by the simulation falls under conditional knowledge ( Flavell, 1985; Schraw and Deninson, 1994).

Regulation of Cognition: According to Flavell, 'regulation of cognition is a systematic process of regulating and controlling own cognitive activities including planning, information management strategies, comprehension monitoring, debugging strategies and evaluation. Planning refers to the process of setting goals and allocating resource materials before learning. Information management strategies refer to the sequential skills and strategy which are used to process information more efficiently i.e. organizing, elaborating, summarizing and selective focusing. Comprehension monitoring refers to the evaluation of one's learning or strategies. Debugging strategies refer to the techniques which rectify the understanding and performance errors. Evaluation refers to the process of analyzing achievement and strategy effectiveness, which usually occurs after a learning episode (Flavell, 1985; Schraw and Deninson, 1994).

The components of metacognition itself reflect different metacognitive strategies and interventions where the primary focus is given to the thinking of students to a great extent. The use of metacognitive interventions in teaching facilitates students' learning and engages them in deep thinking, enables them to analyze their thinking, and helps to monitor and regulate their cognitive functioning effectively.

Metacognitive strategies and interventions are primarily meant for improving the knowledge of the individuals about the subject matter by asking questions themselves repeatedly. So, these include both improvement and assessment of an individual's knowledge and experience. According to Flavell, skimming a set of directions, paraphrasing aloud, and adding a column of figures are examples of metacognitive strategies that help the individuals to know about their thinking and to regulate their thinking to a great extent (Flavell, 1979). The research study of Zan (2000) on metacognitive intervention in Mathematics at the university level revealed that metacognition is an effective strategy to improve the performance of students in Mathematics. In the study, metacognitive interventions were implemented by focusing knowledge about cognition, monitoring, beliefs and attitude of the students through written and oral assessment. Louca (2008) in the book 'Metacognition and Theory of mind' discussed the models and metacognition and reflected Vygotsky's theory focusing more on introspection (self-observation), which implies that the students are enabled to perceive their cognitive process and make an association between knowledge of cognition and control of cognition. The research paper on metacognition in the classroom by Cubukcu (2009) indicated the relation between metacognitive and selfregulation in the context of the theory of metacognition of Flavell. In the study, metacognition reading strategies were taken into account in terms of planning, monitoring, control and reflection. The Florida Department of Education (2009) published a book on cognitive and metacognitive strategies for teachers for problem-solving in Mathematics. In the book, four important aspects were taken into account, i.e. (1) understanding the problem, (2) developing a plan. (3) implementing a solution plan, and (4) Reflecting on the problem. In the book, different metacognitive strategies were depicted like paraphrase, visualization, cooperative learning and logical reasoning by drawing pictures, figures etc. In the research paper of Fathima and Saravanakumar (2012) metacognitive strategies for teachers and students are discussed. They mentioned that metacognitive strategies for students help them to study about their thinking and reflect on their knowledge and experience. On the other hand, metacognitive strategies for teachers help them to get understanding of monitoring and regulating the thinking process of students. The research work of Mohamed (2012) revealed the metacognition, theory of mind and selfregulation in children. The study revealed a strong and significant positive correlation between metacognition and self-regulation. The research study on metacognitive strategies and test performance done by Nett et al. (2012) revealed different cognitive and metacognitive strategies concerning test performance and learning behavior of students. The 'think aloud' metacognitive strategy was highlighted by the researchers, focusing on self-regulation in the form of planning, monitoring and evaluation. The results of the study revealed that the students using metacognitive strategies are having higher test performance. The research study of Chevron (2014) on concept mapping metacognitive strategy revealed that the concept maps are the means of organizing knowledge and that it is a widespread metacognitive tool. The researcher envisaged that the use of concept maps is very beneficial for teachers and students which facilitates meaningful learning and enables the students to think aloud about their subject matter. The review-based paper of Elis et al. (2014) depicted the research-based gaps in terms of metacognitive instructional practices and analyzed the strategies for promoting metacognitive thinking among students. In the paper, key points were discussed, viz. “engaging curriculum, assessment integration, consistency practices, explicit strategy instruction and verbalizing”. The study prescribed the research to put into practice the think-aloud modeling and diagramming/concept maps/mind map/flow charts as metacognitive strategies (Ellis et al., 2014). The research of Festo and Soby (2014) revealed the components of metacognition, highlighting metacognitive knowledge, regulation and belief. The study reflected that metacognition has pedagogical implications for teachers which facilitates students' metacognitive knowledge and regulation through planning, monitoring, correcting and selecting. The research work of Rahman et al. (2014) on the implementation of metacognitive strategies included cooperative learning, online learning and interactive learning activities. The study revealed that metacognitive strategies are also a means of knowledge construction as propagated by constructivists. The results of the study revealed that metacognitive strategy, i.e., active learning helped students to identify and state research problems easily. The analysis of related literature of Ozturk (2015) on metacognitive training with the reading comprehension of elementary students revealed that metacognitive strategies improve the reading comprehension of students as it involves knowledge of cognition and regulation of cognition of students which facilitates in-depth thinking. The study of Wagaba et al. (2016) on using metacognitive strategies and the qualitative data of the study revealed high metacognitive strategies among the students, and it has a positive dimension in terms of academic achievement of students, most particularly about declarative knowledge. Jarrah et al., (2017) in their review papers investigated the metacognitive interventions in education, specifically in learning English skills by analyzing the findings of 35 research studies. In the study, they tried to find out the research gaps in implementing metacognitive strategies regarding writing, reading, listening, speaking and general studies in particular and English skills in general. Pisacco et al. (2018) investigated metacognitive interventions in the field of working memory and text production among students by taking theoretical assumptions and possible adaptation both in individual and group activities, and found that the metacognitive interventions were the means to improve the behavior and school performance of the students (Pisacco et al. 2018). The research study of Duman and Semerci (2019) on metacognitive instructional practice (MIP) and its effect on metacognitive awareness of prospective teachers revealed that there is a positive effect of MIP on some components of metacognitive awareness. In the study instructional activities like thinking about thinking, selfreflections and reflective questions were implemented through planning, observing and evaluating procedure. The experimental study of Langdon et al. (2019) on the effect of metacognitive teaching strategies on the knowledge of regulation and regulation of cognition as well as learning outcomes of students revealed that there was no significant interaction effect in the study, but there was a significant effect in the knowledge of cognition part.

• The study is limited to the effectiveness of metacognitive interventions in teaching and learning process.
• It is limited to the analysis of the effect size of four important metacognitive interventions, i.e., thinking aloud, brainstorming, self-assessment and concept mapping.
• It is limited to the effect size of Cohen.
• It is limited to the theoretical framework of metacognition prescribed by John Flavell.

The analysis of the above literature revealed that different metacognitive interventions positively influence the learning outcomes of the students at different levels. However, out of the different metacognitive interventions most of the researchers are using concept mapping, brainstorming, self-assessment and think aloud as the significant metacognitive interventions. So, a rigorous discussion was made on these four important metacognitive interventions, with support-related literature and their meta-analysis with the help of Cohen's effect size formula (Cohen, 1988).

5.1 Brainstorming as Metacognitive Intervention

The concept of brainstorming is generally referred to as a group-based activity carried out by the students in the classroom to find solutions to a particular problem; it usually involves the collaboration and cooperation of each member of the group. In this technique, the students' learning occurs in a group with collaboration. In this technique, the group members get a chance to share their thinking before the group and they become able to learn the lack in solving a problem. The experimental result of the research study by Alshammari (2015) revealed that the difference between the students taught by brainstorming strategy and traditional strategy was significant in favour of the experimental group in terms of academic achievement of students' academic achievement, so there was a positive effect of brainstorming strategy. The study of Filgona et al. (2016) on the effectiveness of brainstorming learning strategies on the learning outcomes of the study revealed that the students taught by brainstorming strategy were having better academic performance as compared to the students taught through lecture method, so the study recommended the use of brainstorming strategy in teaching social studies. The research study of Malkawi and Smadi (2018) on the effectiveness of brainstorming strategy in terms of learning outcomes of students revealed that there was statistical significance in favor of the experimental group which was taught through the brainstorming strategy. The study also revealed gender differences in favor of females. Figure 3, shows Metacognitive Interventions in Teaching.

Figure 3. Metacognitive Interventions in Teaching

5.2 Concept Mapping as Metacognitive Intervention

The concept mapping refers to the representation of a concept and its sub-concepts in the form of a diagram or chart. So, concept mapping involves interrelations of concepts in diagrammatic representation which enables students to correlate each concept and sub-concepts. The research of Awofala (2011) on the effectiveness of concept mapping strategy in terms of students' performance in secondary school revealed that the experimental group which was taught through concept mapping strategy differed significantly as compared to the control group, which was taught through conventional strategy. Ogonnaya et al. (2016) conducted a quasiexperimental study to examine the effectiveness of concept mapping teaching strategy and found that the students being taught by concept mapping strategy performed well as compared to the students taught with the conventional method. The research study of Adeniran et al. (2018) on the effectiveness of concept mapping strategy and the result of ANCOVA revealed that the students taught through concept mapping strategy improved significantly with the students taught through the conventional method.

5.3 Think Aloud as Metacognitive Intervention

Think-aloud is a method of knowing, understanding and monitoring the thinking of the students. It helps the students to learn concepts through re-reading and reunderstanding the same. In this process, the students need deep thinking about a particular concept.

The investigation of Jahandar et al. (2012) on the thinkaloud method revealed that the think-aloud teaching method has a significant positive impact on the reading comprehension of the students. The result revealed that the mean scores of the treatment group increase significantly than the control group. The quasi-experimental research of Karvawati (2016) on the effectiveness of think-aloud strategy on the reading comprehension of students revealed that the students taught with the think-aloud teaching strategy had higher means as compared to the students taught with traditional method and the difference between the means was significant statistically. The research study on the effectiveness of think-aloud teaching strategy on the reading comprehension skills of the students revealed that the experimental group, which was taught with the think-aloud method differed significantly with the control group which was taught through traditional methods (Alqahatni, 2015; Sonmez and Sulak, 2018). The research on the effect of self-assessment and think aloud as metacognitive strategies revealed that the students taught using metacognitive interventions performed better than the students taught through conventional strategies. So, think aloud and self-assessment is the effective metacognitive strategies for teaching at the secondary level (Dike et al., 2017).

5.4 Self-Assessment as Metacognitive Intervention

The concept of self-assessment referred to a process of evaluating, judging and recommending one's knowledge, belief and attitude. It is primarily concerned with introspection, self-evaluation, self-verification and selfenhancement. It includes a wide variety of techniques through which the learners become able to describe their strengths and weaknesses. Self-assessment enables learners in thinking about their own strong and weak points. Clift (2015) conducted a quasi-experimental study on the effects of self-assessment of learners on their goal-setting in Mathematics and found a positive impact of selfassessment. The research on the effect of self-assessment as a metacognitive strategy revealed a positive effect on learners' academic performance of students. (Dike et al., 2017). The research of Koumy (2017) revealed that the students taught through the self-assessment technique scored more than the students taught through the traditional method about their knowledge achievement and academic thinking, but the result was not significant at 0.05 level.

Tables 1, 2, 3 and 4 represent the effect size of brainstorming, concept mapping, think aloud and selfassessment on certain constructs as metacognitive interventions, from which it is clear that all the metacognitive interventions are having large effect size, mostly in the case of brainstorming and concept mapping strategy; on the other hand, there is a medium effect in the case of think-aloud and self-assessment techniques.

Table 1. Mean, SD, N and Cohen d Effect Size of Brainstorming Strategy

Table 2. Mean, SD, N and Cohen d Effect Size of Concept Mapping Strategy

Moreover, it can be said that metacognitive interventions are having a positive effect on the academic achievement of students with a larger effect size. Figure 4 gives the overall description of the effectiveness of metacognitive interventions like brainstorming, concept mapping, think aloud and self-assessment in terms of the academic achievement and goal setting of students of different groups.

Table 3. Mean, SD, N and Cohen d Effect Size of Think-Aloud Strategy

Table 4. Mean, SD, N and Cohen d Effect Size of Self-Assessment Strategy

The results of the meta-analysis revealed that the brainstorming teaching strategy is having a large effect size in three research studies taken into account; the concept mapping technique also depicts a larger effect size. But, in the case of one study on think aloud and selfassessment, large effect size is revealed and in the remaining two studies, medium effect size was found. Moreover, it can be said that the studies taken into account reveal a strong positive effect of metacognitive interventions, which is revealed from Figure 4.

Figure 4. Effect Sizes of Metacognitive Interventions

The present study is related to the study of previous studies, where an attempt is made to study the effect of metacognitive interventions on the academic achievement and psychological constructs of students through a metaanalysis approach by finding effect size. So, the present study has implications for students, teachers, parents of students and policymakers as a whole. A strong positive effect size was found on the effectiveness of metacognitive interventions; therefore, the present study recommends using brainstorming, concept mapping, self-assessment techniques in the teaching-learning process. It also gives implications to the policymakers to encourage the stakeholders of education for implementing these metacognitive interventions to a great extent. For parents, teachers and students the present study has the implications that in the education of students, collaborative work is highly essential in educating students, and concept maps are important to understand new concepts easily. Think aloud is of utmost importance to promote the thinking of learners. Self-assessment is the basis of child's knowledge; so, efforts should be made to encourage such kinds of activities among the stakeholders of education.

• More and more researches need to be done to examine the effectiveness of think-aloud as a metacognitive intervention in this 21st century so that the thinking of the students could be developed.
• The effectiveness of metacognitive interventions should be studied mostly in terms of social studies as there are fewer studies in this regard.
• The effectiveness of metacognitive interventions should be investigated by taking some psychological constructs such as self-efficacy, creative thinking and positive thinking amongst students of different levels.
• In the present study, only experimental researches have been taken into account for meta-analysis, so efforts should be put to make a critical review of other related studies.
• Adequate lesson plans should be developed by including these metacognitive interventions, and experimental studies should be done at the primary and secondary levels to make the students strong in thinking right from the initial stage of their learning.

After going through the above discussion regarding the effectiveness of metacognitive interventions viz. brainstorming, self-assessment, concept mapping and think-aloud, finally it can be concluded that all these interventions are having a strong positive impact on the teaching-learning process and also the result of Cohen d indicated large effect in maximum cases, so it is recommended to use and encourage the practical implementation of these metacognitive interventions in teaching and learning at primary, secondary and tertiary levels to a great extent. This will develop the thinking among students, and as a result, the students will be aware of their knowledge and adopt essential measures to overcome their weaknesses and develop the strength to the extreme level.

Acknowledgment

We are very much thankful to Gangadhar Meher University, Amruta Vihar, Sambalpur for providing the necessary opportunities and scope to prepare this review paper.

Funding Details

This research work is a part of the Ph.D. Thesis of the corresponding author, and it is also the outcome of the financial grants given by the University Grant Commission, Bahadur Shah Zafar Marg, New Delhi-110002, India. So, we are very much thankful to the University Grant Commission (UGC), New Delhi, for providing Junior Research Fellowship in conducting such research-based activities.

Disclosure Statement

No potential conflict is reported in this study.