Best school is read the internet for a few months. There's all kinds of forums... Long range hunting, benchrest competition, reloading forums, gunsmithing forums, F class and tactical rifle stuff, wanna be sniper forums, varmint hunting forums, olympic type marksmanship, ballistics, 22 rimfire smallbore competition, Army Sniper Manual, etc.
Start reading and read a lot. You'll quickly notice some stuff getting repeated over and over again. You'll be kinda lost at first but pretty soon it will start making sense. Even if you don't reload (which you NEED to do) you should learn about how and why reloading works. Or any other subject like wind drift, basic rifle gunsmithing, how scopes work, scope qualities, ballistic calculators, caliber options, cleaning, laser rangefinders, spotting scopes, etc.
Then practice what you learn with a 22 or 223 or whatever you have.
Educate yourself, for FREE, way better than a single course ever could ever educate you.