Hi, my son just took his ACT for first time and got a 36 on both reading and science sections and 33 on english, but on math he didn't have time to finish and got a 27 so his composite is 33..... should he take again to try and get his math score up to 30 (that's where he scored on the practice tests, not sure he could do much better it's not his strength). But then not sure he would get the same perfect scores again on the other sections. Don't know if it's worth it.
Most colleges will ignore ACT subsection scores in favor of the composite score in their evaluation process. Unless your son is applying to a tech/engineering school that would be particularly interested in his Math score, it's probably not worth it for him to take the test again to try and raise it a little higher. A 33 is an excellent score that will more than qualify him for admission at most colleges.
The only other circumstance in which he might consider taking the test again would be if he's applying to one of the few highly selective schools with 34+ average ACT scores. I'd recommend checking the average scores at schools where he plans on applying so you can verify that his scores are on par with their standards. Just Google "[name of college] ACT scores PrepScholar," which should bring up a page from our admissions database with the appropriate statistics.