The present study aims to investigate the relationship between students' engagement and achievement, and how this relationship changes across the 4th and 8th grade students in Turkey. TIMSS 2011 data were used for the purpose of the study. 7479 fourth grade elementary and 6928 eighth grade middle school students from Turkey participated in the study. According to the results, the 4th grade students display significantly higher engagement than the 8th graders do. Moreover, both student groups' behavioral engagement has positive effect on science achievement. In terms of emotional engagement trajectories, while the 4th graders' liking science has positive influence on students' science achievement, school belonging has no significant influence. On the other side, the two dimensions of emotional engagement have positive influence on achievement of the 8th graders.