This study focuses on quantitative long-term effects of Supplemental Instruction (SI) in terms of graduation and dropout rates. One of the main aims of SI is to introduce students to effective study strategies and techniques. If SI is introduced at an early stage for new students in higher education, it should therefore be expected that this action will promote timely graduation. This has also been indicated in studies at two US universities--University of Missouri Kansas City and Utah State University. This impact should obviously be of huge interest to any college or university that wants to introduce SI for their students. However, more studies from different settings and environments are needed to be able to generalise the findings from previous studies. This investigation is one such study for students at an engineering education faculty. The results from this study show that SI appears to have a pronounced effect on student persistence, and that the effect increases continuously with increasing SI attendance. A student's chances of graduating from an Master of Science (MSc) engineering program within six years, increases by approximately 20-35% for a student attending all SI meetings in the first semester, compared to a student who does not attend SI. The risk of a student dropping out is reduced by approximately 20-40% if he/she attends all SI sessions. The results also show that all students benefit from attending SI, independent of prior academic achievement and gender.