Class Belt Levels?

As i was driving to work today a question rose up once again. I wonder what belt level is to be within the following classes :

Beginner
Intermediate/Advanced

The only reason why i ask this is because when i went to the beginners class there were a red , brown , black! & of course white belts there! but i don't really understand why there were other advanced belts at the beginners couse ( well maybe they are freshing their memory) but there was all different kinds of belts at both of the beginners classes that i went to this week! I thought that they would have them in a class that would suit them with the level of experience & also what they need to learn in order to move up to the next belt but how can u do that when u have them all mixed in together u wouldn't be able to just teach the whites the basics of whever & then also teach lets just say the blue belts what they need to learn before the testing?

Young Warrior