Group-based software engineering projects are an important part of Computer Science and Information Technology curricula. Fair assessment of individual contributions to group-based projects remains a challenging problem. Peer-based assessment, where students assess their fellow team members, is seen as one answer to this. In this paper we discuss the key aspects that need to be addressed in order to develop a successful peer assessment method. We propose a method for carrying out peer assessments for a large software engineering class. We briefly describe a web-based tool that we have developed to support our method, and comment on our initial experiences in using the tool.