ETA
The math. Most bachelor's degrees are somewhere around 120 hours, admittedly some are more but the minimum is 120.
So, that's 12 hours per semester, full time, and then 2 classes each summer, again FULL TIME. That's it. 12+12+6. 30 hours per year. 30x4=120 so the minimum is 4 years unless they take 15 hour per semester then they can get by without the summer classes.
SO the FACT that your son needs another 24-30 hours to graduate...shocking. Okay? just shocking. Did he take a year off? Most people who don't graduate in May take a couple more classes and graduate in July, or they go that next fall and graduate in December.
No one has to add another whole 24-30 hours unless they change their major AFTER they've already completed their basic classes are in their CORE class area. Then they can realistically add another year because many of the core classes they've taken don't count for their new major. BUT they know going into the new program what will count and what won't. They know this because they sit down with an adviser to officially change their major on paper.
My personal thoughts on this are that dad and other family have made big plans with the intent of celebrating this big event. Since they've just found out they've probably made reservations, bought items, and more. So they are not only out money they have to tell everyone their kid isn't going to graduate, not even in July or December, just not at all this year.
I'd have been mad and yelling at him and saying all sorts of things but it wouldn't have lasted 4 hours. It would last a LONG LONG time and I'd not give him another penny if it's his own fault. The part about just putting off telling everyone is a HUGE mistake. He's known for some time. Didn't his adviser have a graduation meeting with him last fall to make sure his spring enrollment completed what he needed for graduation so he's know since last fall that he didn't have enough hours to graduate...he needs a WHOLE YEAR...that is THE thing. Okay? He's known he didn't have enough hours to graduate in May since he went for spring enrollment. He could have called dad and you to let you know his hours aren't going to work out and to not plan something.
He made the choice to not listen or process what his adviser told him last fall.
If he only needed a few more hours or a couple of specific classes then he'd have still known last fall. IF his grades this semester have been failing THEN HE WOULD ONLY HAVE TO REPEAT THIS SEMESTER, NOT A FULL YEAR!
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Well, you're very lucky the dad is giving you a penny, since he's not legally obligated once his child reaches adulthood. It doesn't matter if he's a millionaire, he isn't obligated to give his son anything, neither are you. Paying for their college education is a super wonderful gift. If dad needs the extra money to pay his bills he has the right to say no more.
I'd say it's on you if you're willing to continue supporting him. If you can't afford to pay for his college then he has choices that rely on his own circumstances.
He can get loans, he can apply for financial aid, he can try and get scholarships, and more.
He's an adult and should be the one that is figuring this out, then coming to you to find out what you're willing to help him with.
You have the right to say you don't have any more money but that you'll try to help him with applying for the student loan part. If he borrows $15K for the year then graduates and starts repayment on time he won't be paying much per month and would be able to get it paid off quicker.