The use of visual aids is expected to have a positive effect on students' learning. However, not all visual aids work equally well. A recent meta-analytic research which examined 42 studies has found that the use of animated visuals does not facilitate learning (Anglin, Vaez & Cunnincham, 2004). The failure of visual aids can be attributed to factors such as violating the congruence and apprehension principle, lacking appropriate control functions, and mediation by individual characteristics. Across the board, researchers note the lack of appropriate user-control functions as the keyfactor.

Interactivity, or the user-control mechanisms of animation, is pointed out as a factor for users to better apprehend the knowledge which the visual aid aims to deliver. The functions of stopping, starting and replaying allow students to reinspect the animation. Consequently, students can focus on specific parts and actions of the visual aid. In addition, animations that allow users to control close-ups, zooming, and speed are more likely to facilitate perception and comprehension (Tversky et al, 2002). This study focuses on creating an animated visual aid with appropriate selfcontrolled functions to better help students' learning of introductory statistics. We consider different levels of interaction for mediating students' individual differences.