This site contains a wealth of information about logical fallacies (flawed logic) and gives detailed explanations of some of the most common forms, which are listed in a menu along the left hand side of the page. Since many of these fallacies go by different names, it might be a good idea to look through a number of entries if you are looking for an explanation of a specific term. Most of this site is written at a fairly high reading level, so older students would definitely get more out of it.