Teacher (or employee employed in an instructional capacity, or instructional employee) means an employee employed principally in an instructional capacity by an educational agency or school whose principal function is to teach and instruct students in a class, a small group, or an individual setting, and includes athletic coaches, driving instructors, and special education assistants such as signers for the hearing impaired. The term does not include teacher assistants or aides who do not have as their principal function actual teaching or instructing, nor auxiliary personnel such as counselors, psychologists, curriculum specialists, cafeteria workers, maintenance workers, bus drivers, or other primarily non-instructional employees.