The focus of this paper is a First Year post-primary mathematics class in which Khan Academy's online exercise platform was used weekly for an academic year. Interviews were conducted with the teacher, and students were surveyed about their opinions of the platform and its usage. Regular classroom observations took place to gain an insight into the context of these opinions. A subsequent survey compared these students’ attitudes towards mathematics classes with those of their peers who were not using the platform. Test scores were compared between three classes (one using Khan Academy; two not) to ascertain whether the platform had any effect on student performance. The platform was found to be an invaluable tool for class management: the teacher was able to provide the capable students with enough work while attending to students in need of support. Students enjoyed their time spent on the platform and the more capable students were able to work at their own pace and tackle more challenging exercises. Test results show that the platform may have a negative effect on student performance in the areas of integers and probability, but a positive effect in coordinate geometry. We comment on the evidence for statistically significant differences in the general results of those using the platform and those not.