Martial arts has no league, no season, and no governing body with real power over your local school, which means the parent does the quality control. Watch a class, count the smiles and the standards, read the contract twice, and check what a black belt takes. The style matters less than whether the adults in the room deserve your kid’s trust.
Done right, this is the longest-running activity on the site: the same kid who bowed in at 6 can be training, teaching, or competing at 60. Few sports can say that with a straight face.