What word does your mother always say?
c.1300, "a gathering of persons, a group gathered for some purpose," from Old French as(s)emblee "assembly, gathering; union, marriage," noun use of fem. past participle of assembler "to assemble" (see assemble). Meaning "gathering together" is recorded from early 15c.; that of "act of assembling parts or objects" is from 1914, as is assembly line. School sense is recorded from 1932.