The final stage of the present study was to evaluate whether the useof class size was an effective practice from the perspective of thedevelopment of performance. Model 1 showed that class size as suchhardly predicts more beneficial development of performance and thephenomenon is explained by the uneven division of students ondifferent achievement levels in classes of different sizes. That is, afterwe controlled for the initial competences, the effect of class size was notstatistically significant. In addition, classes with higher proportions ofstudents receiving support performed lower at the fourth grade, thoughnot quite statistically significantly. However, as already discussedabove, the proportion of students receiving support in class predictedhigher performance at the sixth grade. This might indicate that theplacement of students across classes within schools is somewhatpurposeful. The higher proportion of students receiving support inclass does not indicate that the average development of a class would beslower