Thus, we have the propensity score for treated units (vocational school students) PjW*)and the propensity score for controlsPc2000 (students in other tracks), both reflecting the propensity of being sampled in 2000 for students sampled in 2003 or 2006. We first estimate the performance change for students in each type of secondary school in 2000 and their matched counterparts in 2003 or 2006. Then we compare these performance changes among students from different tracks.