Here's an interesting story from the BBC. Back in March a school in Scotland reported they did an experiment where one set of elementary school students played a Nintendo DS "brain training" game for 20 minutes before regular lessons and another group did not. After many weeks, the group that played the video game before the start of regular school lessons performed significantly better on math tests than the other students.
Thinking those results might be a fluke, they did an expanded study including 600 students at many schools. They just released the results today and it turns out it wasn't a fluke. The students that played the video games for 20 minutes in class each day on average had a 50% better improvement in their performance vs. students that only had regular school lessons. You can read about it in detail here.
Now, it's important to remember the students weren't playing just any video games. They were playing those "brain training games" (like Brain Age) that are specifically designed to improve your cognitive abilities. Don't go thinking that playing some Grand Theft Auto or Call of Duty before class will help your exam scores. Although... come to think of it, my favorite way for preparing for exams in college was to spend my study time right before the exam in the video arcade on campus. I'd study for a while, take a break with some arcade action, study some more, and repeat. Maybe that helped with my test scores after all?