Peerwise is a collaborative web-based system that allows students to create and evaluate a test bank of multiple choice questions. The pedagogical motivation behind this system is that students can learn better if they go through a process of self-reflection (meta-cognition), identify / synthesize / evaluate (higher levels of Bloom taxonomy), and articulate the subtleties in a concise format. Denny et al. (2010) show that students who were most active using the system improved their rank in the class relative to their peers who were less active. This is measured by using the students' final course grade from the previous course as a baseline for their initial class rank, and comparing with their final course grade in the course that involves the use of Peerwise.
Denny, P., Hanks, B., Simon, B. (2010). PeerWise: Replication Study of a Student-Collaborative Self-Testing Web Service in a U.S. Setting. SIGCSE 2010, March 10-13.