He should be swinging from the left side on games. The one taking things too serious is the coach. If the kid feels comfortable on his lessons from both sides, let him try in games. I would let him swing from the left side only on games unless a lefty is pitching and keep practicing form both sides. My son started practicing from the left side at 6 and six months later was hitting from the left side on games. Jorge Posada Sr. one day told his son to go from the left side prior to a game without even trying before in practice. He struck out 32 times in a row ubtil he got his first hit. Posada Sr. said... "son this to prepare you for the Big Leagues , I don't care if you strike out 40 times in a row at 9 years old".