This was literally my stepson a year and a half ago, except he wanted to drop out of his degree to do full time day trading.
He was absolutely convinced he was going to make his living doing it, you couldn't tell him otherwise. He and his friends were all doing the online training for it together. To be fair they spent a lot of time studying and trading on the practice accounts etc.
Aug-December he did actually make, and withdraw from his trading account, about two thousand pounds while trading around his university stuff.
He then had huge plans for the next lot of money he'd make: buying a car, going on amazing trips in the summer etc, and again was threatening to drop out of uni.
Jan - May...he spent a lot of time trading. But his trades didn't work out. He just kept "losing". I think he managed to withdraw a few hundred, but nothing like the thousands he had expected to be raking in. Towards the end I think he was on some sort of roll amassing money where he really thought this was going to be the big win and would give him the money for this amazing summer he had imagined, but...it all disappeared in one bad day. He was absolutely gutted and the scales fell from his eyes.
So, he basically learnt the hard way, but he has actually learnt. It's cured him of this idea that it's going to be his career. Your son probably needs to learn the same way. The marketing around it all is so effective, it really sells the dream.