school (n.1) Look up school at Dictionary.com
"place of instruction," Old English scol, from Latin schola, from Greek skhole "school, lecture, discussion," also "leisure, spare time," originally "a holding back, a keeping clear," from skhein "to get," from PIE root *segh- "to hold, hold in one's power, to have" (see scheme (n.)) + -ole by analogy with bole "a throw," stole "outfit," etc.

The original notion is "leisure," which passed to "otiose discussion," then "place for such." The Latin word was widely borrowed, cf. Old French escole, French école, Spanish escuela, Italian scuola, Old High German scuola, German Schule, Swedish skola, Gaelic sgiol, Welsh ysgol, Russian shkola. Replaced Old English larhus "lore house."

Meaning "students attending a school" is attested from c.1300; sense of "school building" is first recorded 1590s. Sense of "people united by a general similarity of principles and methods" is from 1610s; hence school of thought (1864). School of hard knocks "rough experience in life" is recorded from 1912 (in George Ade); to tell tales out of school "betray damaging secrets" is from 1540s.
school (n.2) Look up school at Dictionary.com
"group of fish," c.1400, from Middle Dutch schole "group of fish or other animals," cognate with Old English scolu "band, troop, school of fish," from West Germanic *skulo- (see shoal (n.2)).
school (v.) Look up school at Dictionary.com
1570s, from school (n.1). Related: Schooled; schooling.