Do you have any verifiable information to back up the claim that test prep doesn't improve scores?
I have a handful of sources that disagree.
https://www.act.org/content/dam/act/unsecured/documents/R171...
https://collegefinance.com/college-admissions/does-sat-prep-...
https://www.nytimes.com/roomfordebate/2011/12/04/why-should-...