“Aeronautics instructor” means any individual engaged in giving instruction, or offering to give instruction, in aeronautics, either in flying or ground subjects, or both, for hire or reward, without advertising such occupation, without calling his facilities an “air school” or anything equivalent thereto, and without employing or using other instructors. It does not include any instructor in any public school or university of this State, or any institution of higher learning duly accredited and approved for carrying on collegiate work, while engaged in his duties as such instructor.