It is hard to find research on the Project Approach. However, it is not so hard to find research on related topics. Here are examples of pages which review research that could be helpful to graduate students working on research proposals in this area of education.
1. Research on the Responsive Classroom
The relevance here is that the project approach has many of the features of responsiveness to the learner that are cited in the list of principles guiding teaching that is responsive to students http://www.responsiveclassroom.org/about/aboutrc.html.
2. The Edutopia web site occasionally offers reviews of relevant research such as this page: http://www.edutopia.org/project-based-learning-research
While the research may not be on the Project Approach specifically there are many factors shared by the classrooms involved in this research.
If you know of useful reviews of research please leave us a comment after this blog.