All of them, you pay some for the classes, If I remember I paid 300/semester for classes which is nothing really. usually your firm will pay your share.

But industry standard groups, unions, people who have a vested interest in having a supply of quality labor so they can do business. Some of the classes are sponsored (especially in smaller places where there's not enough support) and in return, they get to train you on a specific product or just hang a banner and give you a 10% tools coupon.