There are a growing number of studies being done into the impact of games in educational settings. Here are some that I have found useful. If you have come across others that you think are of use to teachers please let me know!
Moving Learning Games Forward: Obstacles, Opportunities & Openness – Eric Klopfer, Scot Osterweil and Katie Salen, 2009.
How are digital games used in schools? – Patricia Wastiau, Caroline Kearney and Wouter Van den Berghe, May 2009.
The impact of console games in the classroom: Evidence from schools in Scotland – Jen Groff, Cathrin Howells and Sue Cranmer, 2010
Horizon Reports: 2010 and 2011
Digital Australia 2012 Report
Good Video Games and Good Learning – James Paul Gee
Digital Australia 2014 Report
Playing to Learn 