Learning in the computer laboratory is an important component when students learn computer programming. In this article, we analyse empirical data on novice students working in pairs in the laboratory. Using an approach inspired by phenomenography and variation theory, we specifically focus on how students' learning of theory and their learning of practice interact. We found that theory-oriented and practice-oriented actions play different, but complimentary and closely intertwined roles in students' learning. In particular, we discuss that students' frequent switches between practice-oriented and theory-oriented actions create a variation that is helpful for learning. This variation adds to the variation the teacher creates. Finally, we discuss how and why frequent switches are important for the successful learning process and we suggest a couple of ways to make it more likely that students make such switches when working with assignments at the computer.