Large percentages of students perform above grade level:

Based on the Wisconsin and California Smarter Balanced, Florida FSA, and multistate MAP data, we estimate that 20–40 percent of elementary and middle school students perform at least one grade level above their current grade in reading, with 11–30 percent scoring at least one grade level above in math.

Moreover, we also found large percentages of students performing well above grade level—more than one grade level ahead. Using MAP data, we estimate that 8–10 percent of Grade 4 students perform at the Grade 8 level in reading/English/language arts, with 2–5 percent scoring at similar levels in math. Relying specifically on the MAP data, one out of every ten fifth-graders is performing at the high school level in reading, and nearly one child in forty at this age is performing at the high school level in mathematics. Because of the MAP test’s computer-adaptive format and high measurement ceiling, these results cannot be explained away by the correction that commonly applies to pencil-and-paper grade-level achievement tests. On the latter tests, a fifth-grader with a ninth-grade-level equivalent score amounts to a ninth-grader’s completing a fifth-grade test. By contrast, a MAP test score that is equivalent to ninth-grade performance is in fact based on ninth-grade content knowledge and skills.

Converting these percentages to numbers of children provides a sobering picture of the number of students who are not well served under the current grade-based educational paradigm. In Wisconsin alone, somewhere between 278,000 and 330,000 public-school students are performing more than a full grade above where they are placed in school. And as mentioned above, in the much larger state of California, that number is between 1.4 million and 2 million students.

Federal and state education policies are largely irrelevant for this huge number of students. Getting kids to grade-level proficiency has been a focus of U.S. education policy and practice for well over a decade. Yet the U.S. likely wastes tens of billions of dollars each year in efforts to teach students content they already know.

This structure centered on age-based grade levels, therefore, needs serious rethinking. One option is whole-grade or single-subject acceleration. Indeed, this is consistent with the literature, which has documented uniformly positive benefits when academic acceleration is implemented thoughtfully. Academic acceleration is particularly beneficial for students pursuing professional careers that require substantial academic preparation and credentialing, a point that has been recognized for more than eighty years. Acceleration would also reduce the difficulty of differentiated instruction because students within a given classroom are selected to be far more homogeneous in ability and prior knowledge than they are in the traditional system.

[...]

The current K-12 education system essentially ignores the learning needs of a huge percentage of its students. Knowing this, twenty years from now we may look back and wonder why we kept using age-based grade levels to organize K–12 education for so long.