Here's my take, FWIW...
Anything that is "official," in the sense that the child covers the material with a teacher and is expected (rather than merely allowed) to progress the next year, would be my preference. If you don't have that "seal of approval," then that means that the child may be effectively
held back the following year. Holding back a GT kid?!?! I have a
BIG problem with that!
Grade skips obviously meet the terms of this test.
Subject acceleration, if it is accepted as a permanent move up to a higher grade level with older kids and that move will be respected every year (like a grade skip in one subject, so a 1st grader goes to 2nd for reading this year, say, and then goes to 3rd when in 2nd grade and so on...) is similarly a workable solution.
OTOH, in-class differentiation--while better than nothing in some cases--is NOT something I would generally accept as sufficient. I think differentiation is generally a lousy policy choice for GT education. All it takes is a teacher in a future year who refuses to acknowledge the past differentiation, and now the child has held-back boredom piled on top of the boredom s/he'd already have had in that class. That's just not okay!
(Can you tell that this happened to our child?
)
Some schools are better than others about maintaining the level of differentiation, and it has been a lifesaver for some kids, so I'm not trying to bash it in individual cases. It's another option, and more options are better than fewer. But it would certainly not be my first choice for my child. I've seen it go bad too many times. It's one of the only accomodations for GT kids that can actually make the situation MORE BORING for the child in the long run.
So to answer your question, IMHO, I'd say any time you can get the school's official stamp that your child is ahead and there isn't some specific reason why it's better for your child to stay in-grade, then either grade-skipping or subject acceleration are preferable to staying within-grade and relying upon the kindness of overworked teachers to differentiate.
