Our D19 just took a diagnostic ACT at the local Princeton Review. He was allowed to bring home the test. It’s labeled “ACT Diagnostic Test”. Does anyone know if this would be an actual old ACT test? Is a diagnostic test any different than a real ACT? The number of questions and the time allotted were the same, but I’m wondering if the questions may be a little different. Thoughts?
Sorry, that would be our S19. I think I didn’t have enough coffee this morning. 
For example, there was no dueling scientist section in the Science part. And Science also have seven sections which seems like more than a regular test.
No, the Princeton Review (and Kaplan) tests are not real tests. They are their own creations, probably to avoid copyright infringement.
Since the questions are not authentic, their tests don’t capture the nuances of real ACT questions.
Nevertheless, you’ll still have a rough idea what you would score on a real ACT
As someone who took the ACT last year, I would highly recommend using The Real ACT Prep Guide book to get a better idea of what the ACT is actually like! 