I’m sorry if this isn’t helpful but I can empathize and agree with proceeding with the 504 plan. Push back on repeating 8th grade. I don’t have experience with your school though.

The end of 8th grade is when everything really ramped up with my son’s ADHD and impulsivity. 9th and the first half of 10th were really bad and there were times I was worried he wouldn’t graduate. He’s smart but the focus was a mess and he seemed so unregulated, no matter what we tried. Of course, this time period also was the time of puberty and a period of intensive physical growth and changes.

Things are much better now in every aspect of life going into junior year. Keep trying things, be your kid’s advocate at school while trying to teach them strategies for independence and try to remember the teen years are a wild ride for many with or without special needs.

I can tell you what we did, in MCPS:

My kid with severe inattentive ADHD, low processing speed, dysgraphia and dyscalculia, as well as hypotonia (low tone) and spatial awareness problems was formally diagnosed in 5th grade.

Meds: he was continuously medicated with various stimulants for his 3 middle school years so he could catch up on everything he'd missed before, academically but also in terms of social, emotional and motor skills. In high school he couldn't take optimal doses of meds anymore, due to growing side effects and habituation, but optimal medication for the three years of middle school was crucial to set him back on track.

Physical and occupational: He'd graduated from PT and OT in elementary already, because his motor issues had been significant and diagnosed as a toddler. Starting in elementary, he took ballet at Maryland Youth Ballet for posture and spatial awareness, and trampoline for core toning and spatial awareness at Dynamite Gym. We tried piano for finger skills, martial arts and swimming but he didn't like those. Team sports were out of the question. I worked at home with him on his handwriting. He can write in cursive and block lettering, not well, but it's serviceable.

Tutoring: writing is particularly impacted in kids with ADHD. He had an excellent writing tutor in middle school who taught him to do close-reading, worked on reading comprehension, and all sorts of writing techniques. We worked with him on math. Then later in high school, he had tutors for the ACT and AP exams.

504/IEP accommodations: we paid 3K when he was 10 then 5K when he was 17 for full neuropsychological evaluations at Stixrud's. I cannot recommend them enough, the reports are well written and suggest accommodations the school can include in their IEP or 504. The elementary school gave him an IEP, which he kept for many years, until he switched to a 504 at the end of high school.
He had access to any co-taught class (with an aide in the classroom), a resource class to finish work and receive organizational support, extended time to hand in assignments and during tests, due to his low processing speed, repeated directions, preferential seating to avoid distractions, use of calculator, typing accommodations for exams, and use of lecture notes in high school.

It was a ton of work on his part and on our part, and a non-negligible financial outlay. We didn't hire an executive functioning coach, since the times he most needed directions was in the morning and evening, outside of normal business hours. We were the ones reminding, exhorting, teaching him how to use his planner, etc... I can't put into words how much mental bandwidth it took to push our son into relative functionality.

But now he's in college and doing relatively well. Your efforts will be worth it, OP.