paedagogy (n.)

"the science of teaching," 1580s, from French pédagogie (16c.), from Latin paedagogia, from Greek paidagōgia "education, attendance on boys," from paidagōgos "teacher" (see pedagogue).

before vowels ped-, word-forming element meaning "boy, child," from Greek pedo-, combining form of pais "boy, child," especially a son, from PIE root *pau- (1) "few, little." The British form paed- is better because it avoids confusion with the ped- that means "foot" (from PIE root *ped-) and the ped-that means "soil, ground, earth." Compare, from the same root, Sanskrit putrah "son;" Avestan puthra- "son, child;" Latin puer "child, boy," Oscan puklu "child."

digraph in certain Greek or Latin words; it developed in later Latin where classical Latin used separate letters. The Latin digraph also was used to transliterate Greek -ai- (as in aegis). When Latinate words flooded English in the 16c. it came with them, but as an etymological device only, and it was pronounced simply "e" and eventually reduced to that letter in writing (as in eon, Egypt) in most cases, excepting (until recently) proper names (Cæsar, Æneas, Æsculapius, Æsop). When divided and representing two syllables (aerate, aerial) it sometimes is written aë.