What is an archaic synonym for "teacher"? I'm looking for an archaic, if possible Early Modern English word for the person teaching in pre-university schools (i. e. High School).
Usher was the term for the assistant to a schoolmaster, in Chaucer among other places. Since the usher was the one who actually did the work of teaching, while the Oxbridge graduate 'masters' busied themselves with research and showing off, it might fit your context quite well.
(Thank goodness the education system has changed since those days, eh?)1
OED s.v. preceptor n., 2.a.
A person who gives instruction; a teacher, a tutor.
. . .
a 1568 R. Ascham Scholemaster (1570) i. f. 12v, The scholemaster is vsed, both for Præceptor in learnyng, and Pædagogus in maners.
So there you have three good EModE options.
I think lecturer (n.) may fit the description too:
1580s, agent noun from lecture (v.).
a talk or speech given to a group of people to teach them about a particular subject
To read is to "pick out words." Meaning "action of reading (a lesson) aloud" is from 1520s. That of "a discourse on a given subject before an audience for purposes of instruction" is from 1530s.
Dominie is more Victorian and perhaps Scots, but may suit your purpose.
How about "schoolmarm": a woman who is a schoolteacher especially in a rural or small-town school