I've just done a fair amount of research on this to try to support clustering of the few gifted kids in my dd's class next year. Turns out the principal did some masters work on that concept and understands the benefits to the high achievers, which is great. The downside is that the research interestingly shows that homogeneous grouping only actually provides a benefit to the high achievers. It has little benefit or detriment to the other kids. So that could make it more of an uphill battle.

Here are some things that I read.

A good summary in Q&A format
http://www.davidsongifted.org/db/Articles_id_10173.aspx

A short one
http://www.ericdigests.org/2001-4/cluster.html

I found looking at the list of references at the end of some of the articles to be good startign points for further research.

This one is really long.
http://www.gifted.uconn.edu/nrcgt/reports/rm99138/rm99138.pdf

A good place for all sorts of papers on gifted ed.
http://www.gifted.uconn.edu/nrcgt/nrconlin.html

good luck.