Successful teaching assistants have many of the same skills and qualifications as lead teachers. Patience, genuine caring for students and their success, and flexibility are all necessary attributes for assistant teachers. As teacher's assistants help with lesson planning, materials requisitions, and equipment set-up, they must have familiarity with state content standards for all areas of education at their grade level(s). As many assistant teaching positions require six months to a year of previous experience working with school-aged children and/or special populations, taking advantage of internship programs in high school or college is recommended.
Source: https://www.teachercertificationdegrees.com/careers/teachers-assistant/