1. Results of Using Algebra Tiles as Meaningful Representations of Algebra Concepts:    This first article shows two experiments done with control groups and algebra tiles.  It also has a few quotes from students that felt as if algebra tiles helped their understanding of the concepts.
  2. A Two-Year Collaborative Action Research Study on the Effects of a “Hands-On” Approach to Learning Algebra:  The second article follows a teacher who used manipulatives with her middle school students.  What is interesting is they monitored the students progress in high school to see if the manipulative lessons helped them in their actual algebra class.