This study compares trends in participation and performance on mathematics and science Advanced Placement exams for student ethnic subgroups in California high schools over a 6-year period. Results indicate that although growth in participation and performance is evident for all subgroups, the rates of increase differ across groups. As minority participation improves more slowly than the participation of other ethnic subgroups, there will be a continued lack of minorities in mathematics and science careers. (Contains 2 tables and 5 figures.)