Many intelligent tutoring systems permit some degree of learner control. A natural question is whether the increased student engagement and motivation such control provides results in additional student learning. This paper uses a novel approach, learning decomposition, to investigate whether students do in fact learn more from a story they select to read than from a story the tutor selects for them. By analyzing 346 students reading approximately 6.9 million words, we have found that students learn approximately 25% more in stories they choose to read, even though from a purely pedagogical standpoint such stories may not be as appropriate as those chosen by the computer. Furthermore, we found that (for our instantiation of learner control) younger students may derive less benefit from learner control than older students, and girls derive less benefit than boys.