Transitioning from wood to metal bat?

Start switching each hitting rep out with his wood then gamer.

The switch to metal won't be a problem. You may find that the Coach prefers them working with Metal since that is what they will be playing with.

My son, while on HS Varsity, stayed with Wood in the Cages (drills, etc) but used Metal when they took "on field" BP or games. Coaches always wanted him to use his metal weapon. By the way, due to the potential for Cold Weather damage, I'd save the "Gamer" for games and use last years Metal for BP etc. My son would't use his composite or Hybrid gamer until game temps neared 55 degrees. Never broke one...

Tell him to hit once with a metal bat. That is all he will need. The hard thing to do is transition from metal to wood, not the other way around.

Wicked -
I agree with the other posters but would like to add...
It's great to work with wood. With the feel and small sweetspot, you are more apt to become a better hitter.
That being said, you will certainly be taking advantage of the larger sweetspot and added pop of the BESR bats, metal or otherwise, during the season.
Each bat has it's own specific weight and balance. Hitting the baseball precisely against a pitcher who is trying to make you do otherwise is a difficult thing. I think players underestimate the importance of really being dialed in to the balance of their own bat. So, I think it is important to make sure that any work with wood close to or in season is followed by several cuts with your game bat.
Ideally, in addition to the wood, you would have two of the same style BESR/metal bats (BBCOR for Calif and college). One older one for BP/cold weather and the other for games. Sometimes the backup metal bat can be found cheap on ebay, etc.
Have a great season.