I get that he plays other sports but strength training once a week isn't going to do too much. That goes for anything. Not going to see real weight loss results if you're only in the gym once a week, not going to get much stronger if you're only working out once a week.
It sounds like he wants to play baseball at the next level. If he wants to do that he needs to wake up early and get to the gym before school or go late at night. That's part of the gig of playing college baseball - putting in extra work. I understand he is young and still growing but he still weighs 125 lbs. You can do great at all the showcases in the world, until he gets the weight up it's fairly pointless.
He should be getting on a calorie surplus now - more food/protein shakes and weight room. Even if it starts with waking up and doing a pushup/pull-up/sit-up circuit at home for 30 minutes. Hockey isn't too kind to the smaller guys either.