Previous studies indicate that the use of pair programming has beneficial effects on student learning. In this article, we present a controlled study that directly measured students' acquisition of individual programming skills using laboratory practice (in which students programmed individually under exam conditions). Additionally, we analyzed other measures of student performance, attitudes, and retention. Our results provide direct evidence that pair programming improves the individual programming skills of lower SAT students, and that students who pair program are more confident in their work and are more likely to successfully complete the course. Results from the four other major studies of the effects of pair programming are reviewed and compared with those presented here in order to draw broader conclusions. (Contains 1 figure, 8 tables, and 3 footnotes.)