We did get accommodations on the SAT, although we didn't get everything we asked for. We didn't have recent enough documentation on his vision issues for them to allow a large print test book, but the recent psychologist's report plus his OT history and the history of using similar accommodations throughout his education was enough for them to approve extended time for writing and math, extra breaks, small group/private testing, keyboard for the writing section, and a large block answer sheet.
We just followed
the instructions for students with disabilities seeking accommodations. Since we homeschool, we had to apply directly instead of going through the school.