Here’s the reality, those 3 hour tests (ACT/SAT) carry a lot of weight for most college admissions and can also help families to get significant merit so I would treat these exams like a high school AP/IB class and spend a significant amount of time planning for and taking these exams. With the college board next year allowing for students to take the ACT in 4 separate parts, at separate sittings you can pretty much expect that the average score in each section is going to rise significantly.
So the bottom line for me is get your kid used to studying for and taking these exams (even practice exams) early so he can “master” the format, content, and speed of the exam. D20 studied for the SAT with her math and english teachers and took the exam in 8th grade with several classmates to get some practice. I think these types of early preparation can help when taking these exams later in high school.
Some kids are naturally great on these tests, my D was not one of those students, she needed lots of practice and ACT tutor help but saw her scores gradually rise as she became better at taking the ACT and scoredin the 99th percentile by senior year.
Lastly, my son is in 8th grade currently and while a bright kid he has some ADHD/Executive Function issues (a pending 504) and we will be working with him a lot starting when he is a freshman next year to be able to confidently take these timed tests.