Holding students back when they do not meet a specific attainment level is common practice in a lot of countries. However, this practice is not without controversy and recent studies point at the negative effects of grade retention, especially in the long-term. The majority of these studies focused on grade retention in primary education. In our study, we focused on the effect of grade retention in Grade 8 on language achievement and academic self-concept. We matched students who were and were not retained based on their propensity to be retained and compared both groups using a growth curve analysis. The basic treatment "grade retention vs. promotion" was extended with the certificate these students received at the end of Grade 8. With this growth curve analysis, we were able to draw conclusions on the effect in the short-term, as well as in the long-term. In the short-term (i.e. the year of retention), it seems that grade retention had no negative effect on language achievement in the short-term, and even a positive effect on academic self-concept in the year of retention. The effects became more negative when we considered effects in the long-term. Especially for language achievement, we found a strong decline in the achievement of grade retainees. We found no negative effect of grade retention on academic self-concept. We can conclude that grade retention has a negative effect on the achievement of retained students in the long run, but has no negative effect on academic self-concept. When we take into account the certificate they received, it seems that following the teacher's advice to change track is a better decision than repeating the grade in the same track.