One of the important developments in the way achievement is used in studies of school and individual influences on learning has been the use of achievement growth rather than a static achievement score as an outcome. As part of a longitudinal study of students' progress through the later years of high school, mathematics achievement was assessed in Year 9 (in 1987) and Year 12 (in 1990). In both year levels students completed a modified version of the Progressive Achievement Test in Mathematics 3A. This test measures generalised mathematical performance rather than achievement specific to students' current studies. Scores at both levels were available for over 1000 students from 22 schools. In addition, as part of the study, students provided information about their attitudes to school, self rated achievement, type of course, approaches to learning and social background. The schools constituted a representative sample of non selective government high schools in New South Wales. Over the period from Year 9 to Year 12 most students improved their scores on the mathematics test. The average gain was just under half a standard deviation but there were differences between the types of mathematics course studied, gender and school attended. There was no significant association between gain score and social background. The paper reports on a series of analyses which examined the extent to which differences in the growth in mathematics achievement were associated with type of course, gender, social background, self rated achievement and school attended.