A year and a half back, when I was in the 10th grade, I did some similar research on the effects of video games on the cognitive skills of students. I specifically designed games for this research. I wanted to further this study to test commercially available video games, but due to lack of support and finance, I could not (I'm still in high school).

You can go through the paper here if you want: http://www.emerginginvestigators.org/2015/01/gaming-cognitiv... OR http://arxiv.org/abs/1504.01665

TL;DR; of the paper: I divided the class into two groups, one that played the video games and one that did not. Two tests were taken - one before the children were allowed to play games and another at the completion of one week. Children were made to play games for an hour daily. The results showed that gaming does improve cognitive skills. I was particularly surprised by the substantial improvement that it led to in scores.

PS: Anyone who wants to take this further or maybe has ideas for implementing this, please feel free contact me. I would love to help you out on this.