In Qatar, as in UAE and Oman - it is not usual to use agencies. You apply directly to the various institutions you have interest in.

www.daveseslcafe.com may be able to help give you some names of reputable k-12 private schools. Otherwise, government schools are graduating to a charter school system that I'm not familiar with and would honestly be wary of just because it is in its infancy (I don't know anything detrimental, but experience in the GCC would probably mean some big problems in the starting out stages - but the Government is behind it and seems to be supporting it for now).
Signature line > "You can't fix stupid"