How do I go from school friends to hang out with guys on the weekend?

I would casually bring up a movie that you are going to with a group of friends. Its important that you bring other people so they won't think you are asking them out on a date. If he is interested in seeing the movie then casually tell him that he should come too. Any activity that involves a group of people is best, because they won't get the wrong impression, and it takes the pressure off.

When you're talking with them at school ask them if they want to meet up some where or hang out over the weekend.