The requirements for becoming a teacher's assistant are different from state to state. In private or charter schools, assistants may only be required to have a high school degree. However, having at least an associate's degree can improve an applicant's prospects. Due to federal mandate, teacher's assistants who work in Title I schools must have at least a two-year degree and hold certification as a teacher's aide or assistant. The typical route to a teacher's assistant career is as follows:
Earn an associate's degree in education, assistant teaching, or a related subject like elementary education.
Complete an internship as a teacher's assistant.
Take any tests required in your state for teacher's assistant licensure.
Apply for your teacher's assistant license.
Begin applying to open teacher's assistant positions.
Many colleges and universities offer associate's degree programs in assistant teaching, early childhood development, and related areas that can qualify prospective assistant teachers for this career. These programs typically include classroom-based internships. As many states and schools require teaching assistants to have experience with children, this is additional helpful preparation for the requirements of this career. Many schools also offer programs that allow you to transfer credits earned during your associate's program towards a bachelor's degree in education, which can be helpful if you later decide to pursue a career as a lead teacher.
Source: https://www.teachercertificationdegrees.com/careers/teachers-assistant/