Early-childhood specialists use the term "developmentally inappropriate" to imply that "premature" exposure and early hard work are harmful and time-wasting. Thus, the term "developmentally appropriate" is generally used to discourage schools from teaching certain subjects too soon, but rarely, if ever, to suggest that subjects are not developmentally appropriate because they are being taught too late.
Psychologists have found that there is usually a distinct rise in children's "processing capacity" between age three and age five. But they have also found that there is a great amount of individual variation in children's intellectual development.
As generally used, the term "developmentally appropriate" is devoid of scientific meaning and lacks scientific authority. It is not scientifically credible, for instance, that learnings which millions of children throughout the world are easily acquiring in second grade should be labeled "developmentally inappropriate" for American second graders. Yet that is precisely what American early-childhood specialists have stated about the teaching of mathematical place value.
The consensus among psychologists is that after age six or so, school-based learnings follow a sequence determined not principally by nature or by chronological age but mainly by prior knowledge, practice, and experience.
Many advantaged children receive in their homes the early practice and knowledge they need, whereas many disadvantaged children gain these preparatory learnings, if at all, only in school. The learning processes involved in the unnatural skills of reading, writing, and arithmetic are inherently slow at first, then speed up cumulatively and exponentially. Because of the cumulative character of school learning, educationally delayed children rarely catch up.
When an elementary school declines to teach demanding knowledge and skills at an early age, the school is unwittingly withholding education differentially from different social classes. As a result, the doctrine of developmental appropriateness, which holds back all students, has had especially deleterious effects on disadvantaged children and on social justice.
and Why We Don't Have Them.