Has your son been preparing for the tests efficiently? Does he rely solely on online prep? I think it is more useful to practice with physical copies of the tests and in a simulated test environment (timed and 3 hours in a quiet room in a library or school, for example). If he is going to retest on ACT in December, then may I remind him that ACT is about speed, about one minute is allotted for one question. For the science section of the ACT, a common strategy is to skip the paragraph, go directly to the question and then consult the data and paragraph if necessary.
I don’t recommend a re-take of the SAT literature subject test, which is a very hard test and hard to study for.
Your son is very mature as evidenced in telling you, “Mom, I want to at least try and give it all I can. I’d rather try and fail, then not try at all”. He is a fine young man and will go far.