As a teaching assistant, you don't need to give lectures or anything, just change your homework, basically once a week, and computers and the like will give college students computer operation guidance. You can also be the invigilator of that exam, just for two hours, watching some children draw pictures to help the teacher maintain class order and so on.

Go to fast food restaurants, shopping malls, supermarkets, etc. These are usually charged by the hour. They may be asked to do it once or three times a week for several hours at a time. They will be arranged nearby, and the time can also match their own schedule. There is nothing to do after school, but note that some need health certificates.