All students have strengths and weaknesses and it is important to focus on weaknesses because lower scores can be raised more easily than higher scores. It's much easier to raise an ACT section score from 20 to a 25 than from 25 to a 30. We focus most on the lowest scores until a new weakness emerges, then we tackle that section.
That said, if a student hits a wall, we move on to another section. For example, a student might begin to plateau in reading comprehension around a score of 25 on the ACT and getting a 27 would require a lot more work. Instead of spending a lot of time moving up 2 points in that section, we'll work on another section that has more potential for quick improvement, like bumping a 28 to a 30 in math.