Another thing worth noting is that with the advent of encryption, VPNs, HTTPS, proxy browsers, the advice to remove his admin is critical, and even then there's more things out there than you can possibly block. You have to use localized software(Something installed on the computer) to properly monitor usage, since any tool at the router level will be easily twarted by any sort of encrypted traffic. So your son can go to google.ca, and search anything he wants, and you'll see simply that he was on google, not what he was looking for.
I don't mean to sound alarmist, but as a parent it really is in your best interest to know what your kids are doing online and not enough people put forth the effort and do the work to ensure that they are aware. There's some stuff out there that will mess youth up pretty bad, and it's always a good idea to know what your teen is using the computer for. Kudos for going looking for the tools you need!