Now this is cool. This study of 41 chemotherapy patients in the peer reviewed journal Clinical Breast Cancer had them playing not exactly games, but "computer exercises" including mentally rotating objects (as in Tetris), word finding (as in Fowl Words), route planning (as in Unlimited Rescue) and puzzle solving (such as Bloxorz) four times a week for three months, which is a lot, but not perhaps as much as kids play.
The games mentioned in brackets are all on the Thinking Skills Club site. Maybe instead of teachers I should be approaching health clinics! (Hmmm...)