Good discussion and also the other thread that cabbagedad started.
There is a misconception about JUCO's. They are the same academic rigor as the four year schools but only offer the first two years of a four year degree. English, Chemistry, Calculus, Physics, etc. etc. is the same as taught at the four year schools.
I know all this from first-hand foolish experience. I goofed off in high school and regret that dearly. I had the ability to do much better. After I got out in the real world, I quickly understood the value of education. I started attending JUCO classes at night and spent five years taking classes like Chemistry, Physics, and Calculus. At the end of the five years, I was accepted into several top Engineering programs with no questions asked other than what were your grades at the JUCO. I spent another five years in engineering school while raising three kids and working full time. I was burning the candle at both ends and at the middle at the same time. I regret the time I missed from my young family but it was a sacrifice I needed to make. After engineering school, I spent another four years in law school after that. I truly understand how valuable an education is.
Here's the good news for the poster in this thread. Your son can use the JUCO experience as a do-over to undo lackluster grades in high school. He can also continue his baseball career at the same time. All these things require effort. Grades are merely a reflection of effort. Yes, some are going to have to apply more effort but it can be done if the WILL is there. Encourage your son to improve his grades and everyone's impression of him will change. His future is not determined by what he does tomorrow but by what he is willing to do today. He can do it (e.g., get top grades and excel on the baseball field). Now encourage him to achieve it.