This is a great way to reach children, and then their parents. Many kids have nothing to do in the summer. All you need is a couple of volunteers to scour the city, looking for bored looking teenagers. Most parents don’t know what to do with their children; wouldn’t it be better if they were in a safe environment learning about Jesus?
This is also a great place to firmly root in the faith your current members. Yes Summer Bible School is hard work for only a couple of months, but the rewards could be the eternal salvation of some kids.