The game itself tells you when to specialize.
If 3B is a possibility for college, it’d be wise to really get training on how to play that position. A lot of college coaches will put a backup SS at 3B over a traditional 3B unless that bigger slower kid can really hit for power and has a cannon arm. You need to be defensively as skilled as a MIF playing third. It depends on the program but many college coaches will put a lesser hitter at third base who is fast and great on defense.