Consider a design with two time points corresponding to a pre (T1) and post test score (T2) and two groups (e.g. L(earning) D(isabled) and General Population).
Two common hypotheses of interest can be tested using ANCOVA and Repeated Measures ANOVA and formulated by multiple regression equations as below.
ANCOVA : T2 = intercept + A*group + B*T1
ANCOVA asks "How do the T2 means differ between the two groups over and above what is predicted by the T1 score".
RM ANOVA: T2 - T1 = intercept + C*group + D*T1
RM ANOVA (with a covariate) asks "How does the mean difference in time points differ between groups over and above what you would expect from the T1 score". The group and T1 regression terms are outputted in the RM ANOVA respectively as the group x time interaction and T1 x time interaction.
The below discussion of ANCOVA and Repeated Measure ANOVA is taken from here.