In 2009, four mathematics subjects were offered at the year 12 level in the Victorian Certificate of Education (VCE). The two subjects at the intermediate level--Mathematical Methods and Mathematical Methods CAS--run in parallel, that is, a student can be enrolled in only one or the other, the choice being made at the school level. The curricular content of the two subjects is virtually identical. The difference lies in the type of calculator that students use in class and in examinations. Students enrolled in Mathematical Methods use a graphics calculator; in Mathematical Methods CAS, the more sophisticated computer algebra systems (CAS) calculator is used. The years from 2002 to the present have provided a unique opportunity to observe and compare the patterns of enrolment and achievement in the two parallel subjects. Of particular interest has been the comparison of the patterns for male and female students since previous research findings suggest that females might be disadvantaged by the use of the sophisticated CAS calculator. This article presents a study which determines: (1) if boys' and girls' achievements in the two parallel subjects, differed; and (2) if the difference in the type of calculator used in the two subjects might be implicated in any gender differences identified. (Contains 11 figures.)