'schoolmistress' originates from a combination of English elements 'school' and 'mistress'; 'school' ultimately comes from Latin 'schola' (via Old English 'scolu') meaning 'school', and 'mistress' comes from Old French 'maistresse' (from Latin 'magistra') meaning 'female teacher or woman in authority'.

'school' developed from Old English 'scolu' (from Latin 'schola') into Middle English forms such as 'scole' and then modern 'school'; 'mistress' came into English from Old French 'maistresse' (Middle English 'maistresse'/'mistris') and evolved into modern 'mistress'; the compound 'schoolmistress' appeared in Modern English as the combination of these two elements to denote a female teacher.

Initially 'mistress' could mean a woman in authority or control (not limited to teaching); over time, in compounds like 'schoolmistress' its sense narrowed to mean specifically a female schoolteacher, so the compound's meaning settled as 'female schoolteacher'.