What are the rules for teaching racing starts?

Under Article 103.2 (a mandatory rule for all competition and practice):

• Teaching depth: teach all racing starts, from blocks of any height, backstroke ledges or the deck, only in water at least 6 feet (1.84 m) deep, measured from 1.0 m to 5.0 m from the end wall.
• Supervision: teaching must be under the direct supervision of a USA Swimming member coach. "Teaching" covers everything until you certify the swimmer as proficient, plus any later instruction that changes their basic technique.
• Before certification: all racing starts must be in the water, without the backstroke ledge, whatever the pool depth.
• After certification: swimmers can practice racing starts in water 4 feet (1.22 m) or deeper.
• Shallow starting end (less than 4 feet): in practice and competition, swimmers must start in the water, and backstroke ledges aren't permitted.

Local, state or municipal rules may set stricter depth limits.