Recent research has provided evidence that students' computer use at home is positively associated with their performance at school. However, most of the previous studies have failed to take into account the multiple determination of school performance and, in addition, to explain why using computers at home should benefit students' academic achievement. The study described in this article takes a step towards filling this gap by circumventing the theoretical and methodological problems of previous research. First, we analyzed students' home computer use and their performance in mathematics while accounting for other factors that have been found to affect students' achievement. Second, we investigated possible differences in students' school performance depending on how they used the computer. Based on the data from German students who took part in the Programme for International Student Assessment (PISA) in 2003, our results showed that students' access to a computer was not linked with their performance in mathematics. In addition, it did not matter how often students used a computer at home. A positive effect on mathematical achievement was, however, observed for a small group of students who used the computer in a self-determined way that largely engaged them in problem-solving activities. Overall, the findings indicate that for the majority of students the computer had no substantial influence on their academic achievement. At the same time, the results are suggestive of ways in which performance in mathematics might be enhanced through the use of computers.