As with most arguments on this site, the truth is firmly in the middle. An elite athlete in the 4th grade will usually still be an elite athlete in HS and beyond. That may or may not translate to the field depending on their commitment and lax IQ. The best PLAYERS in 4th grade frequently aren't the elite athletes though. Watching my older son I've seen many of the top players fade out and move down to lower level teams. Over time everyone develops core skills and pure athleticism drowns out much of the skill differences.
With that said, an elite athlete in 4th grade that is also already a top player, will rarely fade away unless they choose to focus on another sport. | 
