This site has great skills tests that could be a supplement to a music theory class, which is what this site is based upon. It covers such topics as pitch, scales, rhythm, chords, intervals, and melody. This site will really test your abilities going from very basic concepts to much more complex concepts. You need to have a good ear on the aural part of the skills test. I would not use this site for music students that have never had any training. Each part gives you a certain number of questions. Depending on whether you answer it right or wrong, a tone will sound and then you will go to the next question. At the end of that session it will tell you how many you got right.
You really need a high speed connection to the internet to view these pages without getting aggravated. Each session opens up in a different window which you can close at the end of the session. You will need the java applet in order to view and hear the test. I wish that they would use a voice saying "that is correct" or "please try again" instead of the annoying little beeps and rings when you get an answer right or wrong. You also need a good set of speakers for the aural part of the test.