Give him a few years of digging ditches and maybe he'll be ready for college again. I failed four courses in my senior year of high school. No way was I ready for more school. But after 8 years in the military and two of trying to find a job after I got out, I was ready for school again. The time between high school and college made all the difference in the world for me. I graduated from college Summa Cum Laude.
Some kids just aren't ready for college straight out of high school. The thing is, many of them never try it again once they've dropped out. They get a job and grow into it and take on other responsibilities (read: family), and they never go back. Nothing wrong with that either. Lots of folks become quite successful without college degrees, especially in the trades. Too many kids go to college because their parents pushed them into it. If the kid isn't ready, it can be a monstrous waste of time and money.