With a 4.0 HS GPA and 28 ACT, it looks like the student already qualifies for a few of the automatic full rides in http://automaticfulltuition.yolasite.com/ ; taking a gap year to work to earn some money while retrying the ACT and taking the SAT to get higher scores will gain eligibility for more of the automatic full ride scholarships. The full tuition scholarships can also be viable if the parents can make a small contribution or if he gets enough Pell grant.
Beyond that, there are competitive full rides that he may also have a decent chance at. See http://talk.collegeconfidential.com/financial-aid-scholarships/1461983-competitive-full-tuition-full-ride-scholarships.html and http://talk.collegeconfidential.com/financial-aid-scholarships/1678964-links-to-popular-threads-on-scholarships-and-lower-cost-colleges.html .
If he wants to go down this gap year path and apply as a frosh to a new merit-seeking list of colleges, he must not enroll in any college courses after high school graduation, in order to preserve his ability to apply as a frosh (as opposed to a transfer, where far fewer merit scholarship opportunities are available).