@Undercrackers I believe the more times you can afford/ tolerate taking the SAT’s / ACT, the higher the probability you have of experiencing a random jump (or decline) in a score.
It happened with both my D’s. Older D went from a 660/670 to a 780 on the writing section of the SAT for one sitting . She also randomly went down to a 24 on reading in one ACT sitting (all the other times scoring a 30 or the equivalent.) She also scored MUCH better in ACT math. 35 vs 650.
Younger D went up from a 650 verbal to a 720 on her final sitting for the SAT.
In all of these cases, there was no additional test preparation involved. In my opinion, the tests are flawed and the more times you take them, the more you might get the opportunity to do better.