(a) The department shall periodically reexamine each child under its control, except those on release under supervision or in foster homes, for the purpose of determining whether a rehabilitation plan made by the department concerning the child should be modified or continued.
(b) The reexamination must include a study of all current circumstances of a child’s personal and family situation and an evaluation of the progress made by the child since the child’s last examination.

(c) The reexamination of a child may be made as frequently as the department considers necessary, but shall be made at intervals not exceeding six months.