One of the most claimed links in the health and education literature is that education prevents from the risk of overweight, and the negative link between education and BMI is up to now out of questioning. More educated adults tend to have lower body mass index (BMI) and a lower risk of overweight and obesity. However, recent literature started questioning the mechanism behind this education gradient in BMI. A more recent and alternative explanation is that the BMI-education gradient hides a selection mechanism, which makes adolescents with higher BMI are less likely to plan for, attend, and complete higher levels of education. In this paper we test for the selection mechanism behind the link between education and BMI by estimating the impact of adolescents' BMI on medium-long-term educational expectations and short-term school choices, while controlling for the potential endogeneity of BMI. Our IV estimates indicate that individuals with higher BMI have lower academic aspirations and are less likely to attend high school after finishing compulsory education, which is a pre-condition of the intentions to go college. These results support the selection (reverse causality) mechanism.