*facepalm*
Oh God, College!
I had a professor that graded on a curve. One uber genius turned a decently challenging and rewarding class into HELL. This kid got 110% out of 100, and then became the only one to pass the class. I repeated the class, and as Murphy would have it, another genius was in my GD class. Failed again. Talked to the Dean, and proved that her curve was impossible, with a 99% fail rate, and the Dean still ignored it.
I then got together with the 99%, and we all petitioned the Dean to have the professor do a "makeup" exam, just to prove we did know the curriculum, but just couldn't pass with her curve(I am NOT kidding, ONE missed question failed you).
He agreed, and the professor fought and waffled, but once the exam was made up and we all took it(without the benefit of the ge3nius spiking the curve), the Dean did see that we all knew our stuff. In our case, which was in the extreme range of rare, the Dean worked with the Dept of Edu. and got us our funding due to, "Scholastic differences"--his polite way of saying the Professor was sucking up to the geniuses, and ignoring everyone else.
(BTW, years later, my brother has been one of the geniuses that the ball-busting professor sucked up to, and he took it to the Dean himself that he thought the curve was unfair, and that she was courting geniuses, and in his opinion, failing promising students because they couldn't get 100% every time. Did I mention I am really proud of him?)
I cannot stress enough that this case is UBER RARE, and most professors grade fairly, and their curve is somewhere in the standard realm of normal.
Talk to your son. Ask him how things are(be supportive). If he thinks it is wrong, he needs to have it looked into fast.
Please don't let money be an issue. I've seen too many promising kids quit school because of the phrase, "I'm paying for your school...(ad-lib lecture here)". Let him know you support him, and ask if there is anything that you can do to help, say like a quiet environment for study, or healthy food to eat while he is studying(standard college students diet usually consists of inedible junk food that sits heavy in the stomach, or ramen, that flies away two seconds after you eat it).
Perhaps he is hesitant on hiring a tutor because he is afraid you won't approve of it's necessity.
Be his advocate,
Be his peer,
Be his friend,
and Be his parent.
Be objective(it's not easy, but step outside your skin for a moment, and speak as though you are NOT his parent, but a supportive peer, seriously, try it. Nothing opens mouths more quickly than you not acting like a worried parent).
Be encouraging. Even and especially if he needs to change majors. It's a students nightmare when parents pay for school.
Be positive. Even when inside you are freaking out.
Be supportive. I'm not talking about mere finances.
Be informed. Not by being nosy, but by properly asking the right questions at the right times.
Be there. Just letting him know you are there when he needs you is often enough for him to open up and voice his fears.
College is a madhouse, with temptations, helter-skelter curriculum, peer pressure, pleasant looking distractions. Add to that the double edged sword of being an adult, having to learn budgets, etc., and the power of not having to answer to anyone, and you have your typical Freshman/Sophomore dichotomy.
Be not afraid.
Just my 2cp.