My coping strategy was to cause large amounts of disruptive trouble, generally go my own way and not pay attention, and then when I learned to read in grade 5, read books about physics and whatnot (I wish I'd found better books).

The best thing that could have happened to me at that age was a good mentor to build stuff with me and point out what I didn't know, a wider variety of better books, and a computer programming environment.

I guess the weakness of the above is that it doesn't build skill. Foundational skills and knowledge (socializing, reading, writing, programming, math, science, engineering, and business) need to be drilled.

The public school system is a write off. Treat it as glorified babysitting. Equip the kid with interesting things to read and hard problems to practice on during class.