ExplaNet is a web-based, anonymous, asynchronous explanation-sharing network. Instructors post questions to the network and students submit explanatory answers. Students then view and rank the explanations submitted by their peers before optionally resubmitting a final and revised answer. Three classroom evaluations of ExplaNet showed that by using ExplaNet students improved comprehension and retention of difficult concepts. Students who viewed peer-authored explanations between submitting explanations showed greater improvement in submission scores and scores on individual final exam questions than students who did not. In addition, ExplaNet recommends a small subset of explanations to each individual student based on student characteristics and preferences. The recommendation algorithm successfully predicted preferences for student explanations in two classroom trials. (Contains 9 figures and 8 notes.)