This applet is designed to explore the relationship between between a pure and stats module marks (a thing of the past) and the strength of correlation. Note: text/symbols displays better if downloaded.
Manipulate the data points and observe the effect on the correlation coefficient (r) which is a measure of the strength of correlation (between 0 and 1). Displaying the means and the means difference will help to rationalise how the correlation coefficient is calculated. Calculating correlation coefficients is not on the new A-level spec. but it may be valuable to understand how it is calculated for more able students. See also the following applet "Interpreting correlation - the effect of re-scaling".