Abstract : Looking at the famous French elite preparatory programmes called « Classes préparatoires aux grandes écoles » (CPGE), this research aimed to study the effectiveness of their training. The objective was to know if students from science CPGE develop specific behaviours that lead them to a better academic achievement in further engineering programmes (internal effectiveness) and a better professional career after graduation (external effectiveness). For comparison needs, the empirical approach focused on engineering schools enrolling both students from CPGE and students from other two-year programmes (DEUG, DUT, BTS). For assessing internal effectiveness, two surveys have been conducted; one directed at students' learning strategies and competences during their initial two-year track and one at their academic achievement in the following engineering programme. For assessing external effectiveness, wages of graduates from engineering schools have been compared. In the end, our data do not show specific learning strategies but with regard to self-assessed competences a significant distinction appears indicating that students from CPGE are more efficient at work organization and learning, for instance. However, they do not show a better academic achievement during engineering training. But the comparison of wages, used as a proxy variable for the professional achievement, indicates that, on average and three years after graduation, the wages of engineers from CPGE is 3,5% higher.