Section 7B. An apprentice, as defined in section eleven H of chapter twenty-three shall, upon the concurrence of the commissioner of labor and industries, be approved by the commissioner under the direction of the state board for related vocational-technical training in any city, town, regional district or independent school, regardless of residential qualification. Related classes for an approved apprenticeship program shall be conducted in a single school system, unless the commissioner, in agreement with the commissioner of labor and industries, determines that it would be in the best interest of said program to conduct such classes in more than one such school system.