Police are investigating after an Instagram video surfaced of an Aldine Nimitz High School substitute teacher being knocked down by a student.In the video, a 16 year old male student who's nearly twice the size of the 66-year-old teacher bumps her twice, then shoves her to the ground as other students look on in a science class at the school.The substitute teacher, who is a retired Aldine teacher, was treated at a local hospital and released.The student was arrested and charged.