ACT (with the writing component) scores are accepted by every school as an equal alternative to SAT1 scores. IVY’s also require 2 (sometimes 3) SAT II tests.
My S said the SAT II’s were more like the ACT’s in that those tests measured knowledge acquired through courses taught (concrete things). He only took the ACT plus SAT II’s; though he did begin SAT 1 preparation (including several practice tests). He thought the ACT was easier than the practice SAT 1 tests because the ACT was more concrete; he thought the SAT1’s were more abstract.
So, while the ACT is not per se easier, students may do better on it (or vice versa) than the SAT 1. In other words, good scores on one (or lower scores) are not necessarily indicative of good (or lower scores) on the other. (You can prepare for the ACT’s by getting one of the ACT prep books – understanding the format and time constraints [the ACT is lots of problems in a short amount of time] will really help [the ACT does not subtract points for a wrong answer; the SAT 1 does]. The more he practices, the more comfortable the testing environment will be – sort of like baseball!)
He should continue to promote himself to his academic schools. He should tell them he is taking the ACT (and take it as early as possible in the fall – the schools may not use one of their precious official visits until the coach knows he can get through admissions). He should also broaden his school selection just in case the scores do not increase.
If you have not done so, take a look at the IVY “athletic index” (AI) to get a feel for the IVY standards for athletes. (There has been much discussion on whether and how much the academic standards can be “lowered” [it’s all relative of course] for athletes in IVY league schools. You can decide for yourself on this point.]
Also, be aware of a potential trap with academic D-3’s and going the regular admission route. In many of these D-3’s (MIT comes to mind), an athlete applies RD and literally doesn’t know until the admission decision day whether he is in – and that is too late to develop a thoughtful back-up plan [though I know of many baseball players who were recruited by top tier academic institutions after they graduated from hs].