Thesis, Nijmegen. On the basis of data from thousands op pupils in the Dutch upper levels of secondary education (i.e. HAVO and VWO) van Langen offers a number of explanations for the lack of participation in maths and science studies by particular groups of pupils, including girls and the children of lower educated parents. In addition, the association between sex differences in achievement and choice of study is examined with the aid of data from more than 42 countries.