(a) No school in any school district having an average daily attendance in excess of 250,000 shall have at any time a certificated teaching staff, excluding substitutes employed pursuant to Section 45030, of whom more than 5 percent have only an emergency credential.
(b) This section does not apply to emergency credentials for bilingual education or for education of the learning handicapped, severely handicapped, physically handicapped, or to any other emergency credential established for the purposes of special education.