This is the question that saves parents money, so let me give you the straight answer.
If your son hits line drives in the cage and looks lost in games, the swing is fine. Something else is breaking down, and every dollar spent rebuilding a swing that already works is a dollar spent on the wrong problem. I have watched parents pay for three different hitting coaches in two years, and the kid’s cage swing kept getting better while his game average kept dropping. Nobody ever asked what he was thinking in the box.
Here is how you tell the difference yourself. You need two data points: the cage and the game.
A swing problem shows up everywhere. He mishits the same pitches in front toss that he mishits on Friday night. His bat drags or his front side flies open whether anyone is watching or not. It is the same in both places. That is mechanics, and mechanics need a swing coach.
A decision problem only shows up in games. The swing looks clean on Tuesday. On Friday he takes a fastball down the middle, chases sliders in the dirt, and swings at 2-0 pitches he should have taken. The hands work. The plan does not exist. That is the strategic side, and no amount of tee work fixes it, because the tee never throws a changeup.
The tricky one is the mix. Some kids have both. The way to sort it: fix nothing for two weeks and just chart. Write down every at-bat. What was the count, what did he swing at, what did he take. After twenty at-bats the pattern will be obvious. If the misses cluster on pitch selection, it is decisions. If they cluster on contact quality against pitches he should handle, it is the swing.
One more thing, and I say this as someone who loves swing coaches: be careful who you hand this diagnosis to. A swing coach sees swing problems. That is his lens, and he is not wrong about what he sees, but he is answering a different question than the one your kid is asking in the box.
If you want an honest read on which one it is, that is the entire point of my $199 Strategic Hitter evaluation. I chart the at-bats, separate the swing issues from the decision issues, and hand you a written profile so you stop spending on the wrong fix. Book it here