Kevin sits in the same position for several hours at a time, then begins rocking back and forth constantly. kevin is most clearly exhibiting a symptom of schizophrenia.

I believe the naswer is: Catatonic symptom

Catatonic symptoms of Schizophrenia would include every small behaviors that caused by abnormal sense of excitement in the patient.
This would include symptoms such as racking back and fourth, inappropriate giggling, tense muscle while maintaining same position, etc.