I went through the American Fitness Training of Athletics (AFTA). You can do a search online for them. The most reputable, that I've heard of though, is the American Council on Exercise (ACE). AFTA is done entirely online. ACE sends you material. You study it, then take the exam at the nearest major city where it is given. ACE is considerably more expensive than AFTA, but I'd say it's worth it. If I could do it all over again, I'd get an ACE certification.