This topic is probably a little too obvious. Of course, if you play rather than study, you won't do as well on the test. However, this could be an interesting topic if you went further than that and talked about the effects, or consequences, of never paying close attention to your studies. What are the long-term consequences of neglecting to study for tests?
Do you have any suggestions for "What is the cause of the recent trend in Ethiopia of teaching children by using plasma TV? What effect has that had on the education of children in that country?" as a cause and effect essay topic?