We all stand out in the parking lot, the teacher gives us sticky notes that have numbers written on them, but we aren't allowed to look at our own number, we put them on our foreheads so others can see them. When the experiment begins we all walk around and look at other peoples numbers stuck to their foreheads, we all want to find the highest number that will accept us as a partner. If you have a low number you subconsciously pick up on peoples rejection, if you have a low number you subconsciously pick up on peoples desire, by the end of the experiment everyone self sorts such that people are closely matched, 20-23, 12-14, 6-8. Although, one thing I forgot is there is the odd 9-22, but I think those are explained by their mutual lack of finding a partner as happens in real life, less common but still true.