When the series first starts Cory, Shawn, and Topanga are in 6th grade and Eric is in 10th grade. When Season two starts they are in 7th grade which means Eric would be in 11th. We know that the age difference between Cory and Eric is 4 years. At the end of Season 3 Cory, Shawn, and Topanga are leaving 10th grade and Eric is graduating. Now I know that not much time has past and Eric couldn't have failed so badly that he was held back for two years. If the producers actually spent the time to realize this, the kids should be graduating in the 7th season, and the show should have gone on for 9 seasons. Also, in season 4 Cory says he was 13 when Topanga kissed him. This episode happened when they were in 6th grade, when he was 11.