The effectiveness of intelligent tutoring systems at increasing learning might be improved if the systems were combined with collaborative activities that encouraged conceptual elaboration. We extended the Cognitive Tutor Algebra, an intelligent tutoring system for high-school mathematics, with a peer tutoring activity that was designed to encourage interaction, reflection, and accountability. Two types of domain support were provided: adaptive support, which used the intelligent tutor domain models to provide feedback to the peer tutor, and fixed support, which simply consisted of answers to the problems. We compared the two peer tutoring conditions (adaptive or fixed support) to individual use of the cognitive tutor (without peer-tutoring activities). Even though students in the individual condition solved more problems during instruction, we did not find significant differences between the individual and collaborative conditions on learning. However, we found a correlation between tutee impasses and tutor learning.