When a Computer Algebra System (CAS) is used as a pedagogical and functional tool in class and as a functional tool in exams, its effect on student achievement can be quite profound. The timing of when students are first introduced to a CAS has an impact on gains in student achievement. In this action research project, the CAS calculator was introduced to students and used to varying degrees in Years 10, 11 and 12. The effects on students' final year results were examined in terms of the timing of the introduction of the CAS device and the extent of its use in the classroom. There is some evidence of greater improvement in learning by introducing the calculator in Year 10 rather than Year 11. This gain is evident for low, average and above average mathematics achievers.