The phrase "to teach the assistant" means to provide knowledge or instruction to an individual who helps or supports you with tasks or work. You are helping them learn and become better at their job or role. Full definition
While there will be some differences depending on the requirements of the class being taught, many tasks are similar for graduate teaching assistants whether their area of interest is English or biology. (jobhero.com)
Students serve as teaching assistants for a mathematics education course. (bu.edu)
Many applicants work as teaching assistants or as assistant educational psychologists at local councils. (newscientist.com)