 Sample size calculation is based on the primary endpoint mean of the SKAMP Combined score over all time points in the classroom setting. The study should have sufficient power to detect a difference between treatments if a moderate effect size corresponding to Cohens d0.5 were present in parallel-group study in two independent patient groups. Assuming a correlation between measurements in the same patient of 0.6, this translates into an effect size of 0.56 in a cross-over trial comparing within patient measurements. With this effect size, 27 patients have to be included in the study, to achieve a power of 0.8 at a two-sided significance level of alpha0.05. To account for a small number of drop-outs, 30 patients have to be randomized. 