Edutopia, which is sponsored by the George Lucas Educational Foundation, has an engaging new teacher guide that can help teachers design and assess project-based learning.
The Top 10 Tips for Assessing Project-Based Learning is a colorful PDF you download at the site. The tips are organized to follow the progression of a project. First comes the planning, then the launch into active learning, ultimately leading to a culminating presentation. Reflection is the critical final stage. The guide also includes a bonus tip: How to assemble your own PBL toolkit. The 14-page guide contains links to many resources to help you develop the PBL process.