If you do a google search for "UK Tier 4 visa sponsors" you will find a list of all currently authorized (2016) sponsors. The list includes CTC but does not appear to include OAA (unless I overlooked it).
When the government were tightening up on the issuing of these visas (in about 2008 if I remember correctly) most of the schools decided that it was not worth the effort. There was talk of the approval process including inspections by Ofsted, and none of the schools were keen on this! But things may have improved since then.