"Give up on the idea of “constructive criticism.” Positive reinforcement works better anyway." I've been thinking about this lately. It seems to me that it isn't that simple. It depends:

1) what your objective is...personally, I think the morally right answer is "to develop a productive member of society who's emotionally well adjusted" I'm sure some folks, though, intend to raise the next Tiger Woods (or Britney Spears or Isaac Newton). The latter has a lower probability of success, surely. And most kids who fail to reach the zenith of financial or noteriety success...most of those kids will probably have some serious emotional problems if they've been told that's the objective. But I'd hate to think the world would be without some great invention or entertainment or...just because some folks aren't as conservative, or interested in their kid's psychological well-being as I happen to be.

2) the temperament of the kid. Some kids would be happier knowing things they could do "better". Other kids would be happiest being allowed to just "play", rather than compete.

3) your facility with coaching and the sport in question. Really...suppose I have a kid that has some aptitude with tennis. I know nothing about the sport...best I think I could do (assuming the kid is driven to achieve) is to find an expert to provide "constructive criticism" of his/her athletic performance. Then, I could provide emotional support (not just "positive reinforcement"), to increase enjoyment of the sport. (Heck, Goleman, in his pseudo-scientific way, would likely argue that an emotionally supported child would likely perform better in competition, anyway.)

On another note, I've always heard that kids shouldn't lift weights until age 12 or 13...I think the implication was that lifting prior to their largest growth spurt predisposes their joints and ligaments to early arthritis and injury.