Cal. Code Regs. tit. 5 § 12068
A teacher aide may perform assigned duties while not under the direct supervision of the teacher for a period not in excess of 25 per cent of the time for which he is engaged in the performance of his duties during any school day. The duties which a teacher aide may perform while not under the direct supervision of a teacher shall not include independent control or supervision of pupils except during designated noninstructional sessions. While not under the direct supervision of a teacher, a teacher aide may prepare materials as directed by the teacher, provide personal assistance to designated pupils in the event of an emergency, and visit pupils' homes when directed by the teacher in accordance with school district policy, and perform other duties as assigned by the teacher.
Cal. Code Regs. Tit. 5, § 12068