Wikipedia is not considered to be a reliable source of information for students simply because anyone is free to add or alter information that is posted. With this comes the risk that information that has been added has not come from a reliable source and could be misleading to the reader. Although Wikipedia appears to be a reliable academic website (and I recall being told to use it in high school), it carries great risks and all information taken from it must be checked with other sources to ensure its reliability. In many cases entire stories or pages of ‘factual information’ on Wikipedia have been fabricated by other users, for example I recall a friend of mine posting a page about ‘National Shake Your Booty Day’ because she wanted it to become a holiday. The information posted on Wikipedia is not automatically reliable simply because it is on a website. There is no guarantee that the person posting it knows what they are talking about and it is much more reliable to gain your information from an expert in the field, rather than a stranger.
Because there are no ways of telling if information gained from Wikipedia is reliable, it is simply wiser and easier to avoid Wikipedia altogether. There is no guarantee that the person who posted the information knows much more about it than you do.