How Effective are Parental Computer Controls?

Here’s a post I did a couple years ago describing my set-up. My son, then eight and now ten, has a computer in his own room.

The only update now is that his WAP is running WPA2 now because he has a 3DS, which is WPA-capable. He has a Nook and an iPod Touch, but only access to his WiFi, not the general household one.