I'm Doug, and I'm very sorry to hear of your situation. My goal is to provide you with excellent service today.
I certainly empathize with your situation and the fact that your ex is abusing the system to take you for all she can get. Unfortunately, CA law is quite clear in its support guidelines. Child support is an obligation at least until the child reaches the age of 18. However, if that child is still attending high school on a full time basis---be that attendance at a formal school, an online school or even through home schooling, support does not end until the child graduates or turns 19, whichever occurs first.
Unfortunately, you cannot force your child to attend summer school, and if 55 units is full time, you cannot demand that he earn more in order to graduate on time. The court will not order that he do so either and the fact that he will not or that his mother will not force him to do so---is not a legal basis for the court to terminate support.
I understand that you may be disappointed by the Answer you received, as it was not particularly favorable to your situation. Had I been able to provide an Answer which might have given you a successful legal outcome, it would have been my pleasure to do so.
If you have additional questions, you may of course reply back to me and I will be happy to continue to assist you further until your questions have been answered to your satisfaction.
Would you please take a moment to positively rate my service to you based on the understanding of the law I provided by clicking on the rating stars---three stars or more. It is that easy. That is the way I am compensated for having helped you.
Thank you in advance. I wish you the best in your future,