You should also know that Algebra II is the first weeder course on the path to Calculus.
It is a very difficult class. It wouldn't surprise me to learn that even a HG+ student might struggle with it, particularly if there has been a lack of true challenge previously.
Indeed. Alg II was an eye-opener for me, because I'd never had a prior experience where the teacher used the entire hour, every day, for lecture. This was a teacher with math degrees, he was very thorough, and I left the class every day understanding the material, but that's how much time was needed, because the concepts were that complex. The next day, we moved on to something new. As a student who had never had any challenge in math before, I was unprepared, and earned a C for the first semester, because I wasn't making time to do any of the copious homework (I usually completed that in class before). The teacher wasn't checking it every night, so it was up to our executive management skills to keep up all semester, and my motivation just wasn't there. I wasn't practicing what I was learning, though I was still able to pull low-As on the tests. The homework folder... yikes.
I could easily see a situation in which an LD like dysgraphia would have changed that C to an F.
Another important thing to consider in your DS's case is that if he'd always been told he was a math rock star, and he suddenly finds it difficult, he may be experiencing imposter syndrome, which may be causing him additional emotional issues that get in the way of his intellectual processes. Perfectionism. Self-sabotage.
