Released August 16, 2016 by Johns Hopkins School of Education, Institute for Education Policy:
"How can so many students be invisible? Large numbers of American Students Perform Above Grade Level."
1) Link
2) 16-page PDF

This bit of research is a must-read for all parents and teachers having experience with one or more students who are performing at least one year above grade level.

Originally Posted by Final Thoughts
Currently, the evidence suggests that between 15% and 45% of students enter the late elementary classroom each fall already performing at least one year ahead of expectations
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Knowing this, one day we will likely look back and wonder why we kept using age based grade levels to organize K-12 education for so long.
In beginning to acknowledge the 15-45% of students who are performing one or more grade levels ahead, possibly the 10% reported as 4 years ahead in Reading and the 2% reported as 4 years ahead in Mathematics may also have their academic/intellectual needs recognized and met.

Originally Posted by Implication 1
This begs the question of just what these students are learning from grade-level content in classes organized by age. The U.S. likely wastes tens of billions of dollars each year in efforts to teach students content they already know.
Hopefully this may begin to open doors to widely accepting a policy and practice of aggregating children using flexible cluster grouping by readiness and ability in each subject area, without regard to chronological age so that each child is presented with appropriate curriculum and pacing in their zone of proximal development.

This would better emulate the larger world beyond the school environment as workplaces, hobby clubs, sports teams, etc include a mix of ages.