I do like compacting curriculum quite a bit, as there is less of a concern about gaps, and one can document for schools that everything in the state requirements has been mastered. If you can get the school to do it, it's also relatively easy and affordable, as you simply use the existing materials. In another recent thread, we've briefly discussed pretesting through unit/chapter tests, and giving mastery credit for any unit/chapter with at least 80% accuracy (or 70%, depending on what you and the school decide is best). For lower scores, the teacher teaches through that unit/chapter only.
If the school has both grades, you can also explore cross grading (say for reading into higher, and math into less high) for core academics, and staying with his age mates for content areas (social studies, science) and specials (art, music, gym). For placement purposes, the most straightforward option is to use the school's curriculum in that subject to place into the correct grade level for single-subject acceleration. If there is no placement test in the curriculum, then one can use the same pretest method as for curriculum compacting, until your DC begins consistently scoring below the cut score. At that point, back up to the nearest beginning of a grade level, and that's his cross-grade placement in that subject. (Or, if he's really close to the end of a grade level when he reaches his ceiling, I suppose someone could tutor him into catching up--but I think there is value in placing children slightly below true instructional level for grade skips or SSA, as moving up also involves increased social-emotional and executive function demands, for which he will need to reserve some of his cognition.)
