http://parenting.blogs.nytimes.com/2012/10/14/against-accelerating-the-gifted-child/
Against Accelerating the Gifted Child
By JESSICA LAHEY
New York Times
October 14, 2012

...

According to A Nation Deceived, a 2004 report by the Institute for Research and Policy on Acceleration, most schools cannot handle the needs of gifted children, and acceleration is a good solution for students in need of more intellectual stimulation. The report points to hundreds of studies that have been conducted on academic acceleration, and most show no negative emotional outcomes for accelerated students. But the majority of these studies are based on subjective reporting by the students themselves, a notoriously inaccurate and blunt research tool.

My concerns about grade accelerations are best articulated by the recommendations for best practices published in Gifted Child Quarterly. Toward the end of the report, the author, Maureen Neihart, warns that acceleration “may be harmful to unselected students who are arbitrarily accelerated on the basis of I.Q., achievement, or social maturity,”

In other words, the decision to skip students ahead a grade or two should not be made on the basis of intellect alone. Steve Perkins, a high school teacher in Indianapolis, agreed by e-mail: “Yes, a fifth grader may be able to do seventh-grade math. Skipping the child, however, ignores the physical factors of development. When we assume that the pure cognitive is the be-all, end-all, we have grossly misunderstood the whole.”

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I don't agree with the article, but there are some good comments at the NYT site rebutting it. The educational system often acts like age is the "be-all, end-all", and that is currently a bigger problem than overemphasis of the "pure cognitive" in grade and class placement.