Inphinity:surfisup1000:And, they can just go over to their friends house and you have no idea if they supervise internet access. So, an ISP block sounds more encompassing to me.
... you know they'd be using their friends' internet connection at their friends house, so your ISP filtering your connection will have no impact?
But, the others would also have filtering with their isp , which is the beauty of this solution.