It is based on the theory that learners of the same age at the same level of social and intellectual maturity should be taught at the same pace.
[2] It also forms part of the standardized learning organized in stages and progresses in predictable and known ways.
[2] The concept of age-segregated school is considered a recent historical development, with scholars noting that during the late eighteenth century students of widely varying ages in many European countries attend school together, a practice that was also adopted in the United States.
[3] In colonial America, it was customary to teach students of various ages in one classroom by one teacher.
[1] The graded education was only introduced from 1848 to 1870[4] after several American educators such as Horace Mann were impressed and, thereafter, adopted the Prussian graded school model.