This study examines the academic performance and demographic characteristics of Greek students in elementary and secondary school. It is an extension of an earlier study that was done in a different time frame to support related conclusions. The dataset includes all students in the last two grades of primary school and the first three years of secondary school. The academic success levels, as well as their longitudinal dimension and divergence by demographic factors, were identified. The results of our previous study, which showed that there are four consistent levels of academic achievement across time, were confirmed by the current research. In addition, the significance of demographic characteristics such as gender and guardian occupation were verified. Last but not least, the importance of early identification of low-performing students was emphasized, as was the likelihood of a significant improvement in their performance. We think that one of the biggest problems with making good educational policies is that it’s hard to help students who aren’t performing well.