These schools teach yoga and are also schools for certification on being a yoga instructor. Although certification is not legally required or regulated, many people do get certifications and trainings at known organizations before beginning a career in teaching yoga classes at health centers or local yoga studios. Often they have certifications associated with them. I have not looked into the validification/respectability of each and every certification and encourage you to do that work if you are interested in being a certified yoga instructor. Also, this list is not all inclusive at this time.