As a parent/LC, my biggest angst for my son is the lack of differentiation in assessments. Our school uses 90%+ mc assessments, probably because they are quick and easy to grade. My son rarely sees anything in black or white. He will look at every answer option and determine how it can be relevant. And in most cases, he can make a valid argument for multiple responses. A truly effective GT program needs to be a 360 view - including curriculum, materials, discussion, assessments, etc.
The assessment side is where we have seen most attempts fail completely.