Lant Pritchett and Amanda Beatty argue that many education systems are attempting to push children through curricular material faster than their teachers can teach it and their students can learn it. Students fall behind and eventually stop learning. The authors provide a formal model of this phenomenon and provide empirical evidence on its implications.
Using data from three recent studies in South Asia and Africa, Pritchett and Beatty show that a majority of students spend years of instruction with no progress on basics, in part because curricular paces move much faster than the pace of learning. They construct a formal model that portrays learning as the result of a match between student skill and instructional levels, rather than the standard (if implicit) assumption that all children learn the same from the same instruction.
Their simulation shows that two countries with exactly the same potential learning could have massively divergent learning outcomes, with the country that goes faster having much lower cumulative learning.