Had an ADHD eval, yet?
ADHD has 3 types, and ADHD-I and ADHD-C kids often get missed until puberty (or missed entirely) because we present in a less annoying way that ADHD-H types do.
www.additudemag.com is one of the best sources of free information you can find. CHADD is another one.
Montessori is actually one of the best models for ADHD education in the K12 system (because hyperfocus on things you're interested in comes part and parcel with space cadet syndrome), and it allows you to do multiple areas of study in one type of work (reading, writing, math, and history... all in a science work for example). But upper level montessori requires an organization and completion of boring stuff that a lot of ADHD kids just aren't capable of. (It's far far worse in standard k12, though)
So... here's a thing to know about ADHD-I and ADHD-C. We think more than one thought at a time. Most people I know are thinking of 5 or 6 things concurrently, and have another 2 dozen in the background. It's VERY useful in certain circumstance, but in the day to day grind it can almost be impossible to break through. And then once broken through, no matter how important, it's just not as interesting as the 5 other things, so it falls to the back of the 'rolodex'.
Stimulants slow us down. In ADHD-h & ADHD-c, they slow down our bodies. In ADHD-i and ADHD-c they slow down our minds.
Imagine the most helter skelter tumble of thoughts you've every had. First pregnancy, death of a loved one, anything, ANYTHING where your mind is tumbling all over itself and you find yourself saying "Huh?" when people are talking to you. That's what ADHD is like (in part, there's more to it, but that's a piece) ALL. THE. TIME.
What you've described are CLASSIC ADHD flags. And you're at the classic age for the less annoying versions of ADHD to become super annoying (aka when they most often get diagnosed).
So, myself, I would get an eval. In the meantime, though, check out the link above, and see if it sounds familiar. Remember, there are 3 types. You'd be looking at ADHD-I (formerly ADD), or ADHD-C (formerly add/adhd... the i = inattentive, and the h in the adhd part is because of the hyperactive MENTAL part.... the c is combined, which means both hyperactive mental and hyperactive physical)
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WHY AN EVAL IN IMPORTANT
What you would do that would 'work' is entirely different if your son is neurotypical or if he's ADHD. A common example is if he's neurotypical, he probably needs quiet to study. If he's ADHD, cranking up music will help him study. Two POLAR OPPOSITE methods.
You can pound your head, and his, against the drywall for YEARS trying to do 'what works' on neurotypical kids and failing if he's ADHD. Sorta like telling a diabetic to just CARE MORE about producing insulin. Not going to happen. So the eval is super super important to save you both time and heartache and damaged relationship. Because a lot of things that work on a neurotypical kid make things WORSE on an adhd kid. And vice versa.