1.British EnglishBrE a person who is not a trained teacher who helps a school teacher in classes 教师助理
2.American EnglishAmE a graduate student at a university who teaches classes 助教〔指教课的研究生〕
Examples from the Corpus
teaching assistant• She acts as if she had been employed as confidential adviser, keeper, critic, teaching assistant, and lay psychiatrist.• She was an undergrad at Barnard and he a graduate teaching assistant at the university.