Most of the students, 86% in school A, 72% in B and 85% in C used a higher seat (High mismatch), only 1% of the students of school C used a seat that was too low (Low mismatch). In the case of the High mismatch most of the students will not be able to support their feet in the floor, generating increase tissue pressure on the posterior surface of the knee (Garcı´a-Molina et al., 1992; Gutie´ rrez and Morgado, 2001; Milanese and Grimmer, 2004).