Why is 'grade school' a term for primary school in the …
https://www.quora.com/Why-is-grade-school-a-term-for-primary-school-in-the-United-States-when-middle-and-high-school-also-have-grades
Graded school, also called grade school, an elementary or secondary school in which the instructional program is divided into school years, known as grades or forms. At the end of each academic year, pupils move from one grade to the next higher in a group, with only an occasional outstanding achiever allowed to “skip” a grade, or advance beyond his fellows to a still higher …
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