In 1988, most schools in Western Australia adopted a Unit Curriculum structure in the first three years of high school, following piloting of the scheme in seven schools in 1987. The goais of the Unit Curriculum are stated to be excellence, equity, and relevance, and one of its key features is the increased flexibility students have in making their subject selection. This article reviews the science enrollment and achievement patterns of males and females studying in the pilot schools in 1987, and for the first three years of the operation of the Unit Curriculum in 1988, 1989, and 1990. The data indicate that lowering the age for subject choice is associated with a reduction in the amount of science studies, especially by females, and with the early manifestation of sex-stereotyped subject selection. It appears that if early sex stereotyping is to be avoided, then students need to be provided with more structure in their selection of units. This article emphasizes the need for all involved in system-wide curriculum change to be fully informed of the potential benefits and dangers of curriculum models which allow wide flexibility, especially where curriculum change affects students' “choice point”.