I do believe the cohorts would match better if schools were applying a consistent standard for acceleration, like the IAS. I think there are a lot of parents who would allow their child to be skipped if the school recommended it, but wouldn't go out of their way to advocate for it. This would allow more children of parents with a passive parenting style to make it into the grade-skipped group.
If the IAS assessments were also made available, then the cohorts could be further matched. However, attempting to do that might prove difficult if almost all the students with good evaluations are actually skipped. Perhaps a discontinuity analysis could be performed.
