There are two excellent websites you might try for research on this issue. The National Association for the Education of Young Children may have information that will help you. You can also go to the ; at that site you will find summaries of research articles that I'm sure will address your question.
Another resource would be professors in the education, child development, or psychology department of a local college or university. They could steer you to relevant resources, and might even be able to talk about this topic with school officials or parent groups at your school.