I'm chiming in late here with a bit of a different perspective as I wasn't 18. But when I was 22 and had graduated from college, my dad told me that (1) he was proud of me for finishing in 4 years with a 3.5 gpa; (2) law school was a whole lot harder than college and (3) while he would help with tuition (I also had scholarships and grants), my living expenses were on my own from now on as I was truly an adult at age 22. My undergrad was a state school and I had scholarships to cover almost all expenses, btw.
I found an apt for the fall with 2 other girls and my share for rent, utilities and 1/2 of a garage was $300 per month. So I knew I needed a summer job that would bring in minimum of $3600 to cover my apt. I wanted to make $5000 so I could have gas money and have a little bit of spending money!
My dad and I sat down with the pencil and calculator--the week after graduation. My full-time pool/lifeguard job would guarantee 40+ hours and I remember thinking I would have almost $3000 from that job. My second job of teaching private swimming lessons would/could bring in another $500 to $1000. But I wanted more savings (and a bit to spend during the summer, I was 22 after all!). So I found a 3rd job I could work 2 days a week that would cover my shortfall. By the time I left for law school (my parents graciously let me live at home for free that summer) I had $5600 in savings. I worked 7 days a week, sometimes 9 in the morning to 10 at night. I also had to pay my car insurance and taxes. This was 1998 so costs are different now. I was making max $8 per hour any any of my jobs but I was also working 70 hours a week sometimes.
I would recommend you all sit down and break down the college expenses. I know you said there is a need for $22000 next year. Find out what portion is housing and what portion is tuition. Offer to help either with the housing part or tuition part, which ever you think will motivate him. If he has to pay for his dorm/living unit, he may be more careful with his spending. If he has to cough up his own funds for part of his tuition, it may instill a sense of pride in his education. My dad never "forced" me to work as much as I did that summer but I figured out that I had to work that much to cover my living expenses--I had a healthy fear of not being able to pay rent come next spring and letting my roommates down. My dad and I are exactly the same--stubborn. Forcing anything never works with either of us, LOL. Good luck!