Originally Posted By: MumOfThree
The problem is not lack of ways of assessing whether a child is advanced enough to be accelerated.
Agreed.
The problem is also not a lack of funding, as acceleration is not costly, per the SMPY study.
I believe the problem is desire to create equal outcomes for all (which is as ludicrous as expecting all students to maintain uniform growth in height, and equal height outcomes).

post with article mentioning acceleration - SMPY study (2016):
Acceleration is common in SMPY's elite 1-in-10,000 cohort, whose intellectual diversity and rapid pace of learning make them among the most challenging to educate. Advancing these students costs little or nothing, and in some cases may save schools money, says Lubinski. “These kids often don't need anything innovative or novel,” he says, “they just need earlier access to what's already available to older kids.”