In a letter to parents, Matin Abdel-Qawi called the incident "an aberration, but a severe one." A spokesman said the guard, Marchell Mitchell, 23, was fired the day of the alleged attack.
Mitchell has also been charged with a felony, inflicting corporal injury on a child, officials say. He is free on bail.
Abdel-Qawi said Mitchell and another guard were trying to get students out of the corridors and into class at 9 a.m. on May 19 when the conflict with Francisco Martinez, a freshman at the high school, occurred.
The principal said that when the teenager was slow to respond to his orders, Mitchell pushed the wheelchair. Martinez attempted to slap him away, Mitchell handcuffed him, and the student spat in Mitchell's face.
"The security officer then struck the student several times before dumping him from his wheelchair onto the floor, at which time another security officer intervened to restrain his partner," Abdel-Qawi told parents.