The study illuminates the effectiveness of Co-operative Learning Strategies in learning English Grammar for the learners at secondary level.  Cooperative Learning is particularly beneficial for any student learning a second language. It promotes peer interaction, which helps the development of language and the learning of concepts with content. It is important to assign ELL (English Language Learners) to different teams so that they can benefit from English language role models. ELL learn to express themselves with greater confidence when working in small teams. Jacobs, G. M., & Gallo, P. (1999 February) recommends the co-operative learning in enhancing extensive reading in second-language instruction. Objectives of the study: 1.To diagnose the problems of the learners in learning English Grammar through conventional methods.2.To find out the significant difference in achievement mean score between the pre test of control group and post test of control group.3.To find out the significant difference in achievement mean score between the pre test of Experimental group and post test of Experimental group. 4.To find out the significant difference in achievement mean score between the post test of controlled group and the second post test of treatment given controlled group.5.To find out the impact of Co-operative Learning Strategies in learning English Grammar. Methodology: Rotational group Experimental method was adopted in the study. Participants: Eighty students of studying in standard X from Maruthamalai Higher Secondary school,Vadavalli were selected as sample for the study. Instrumentation: Researcher’s self-made achievement test was used as instrumentation for the study. Procedure of the study: The following activities were designed 1.Positive interdependence.2.Round-Table.3.Face—to-Faceinteraction.4.Write around.5.Jigsaw Team.6.Team pair solo and 7.Think—Pair Share  Findings: Co-operative Learning Strategies is more effective than traditional methods in learning English Grammar for the learners at secondary level. Educational implications: It can be implemented in other levels and all other the languages learning.