No power or duty conferred or imposed by this Act on the Secretary of State, on education authorities, on parents or on young persons shall be construed as relating to any child or young person who is employed by or under the Crown in any service or capacity with respect to which the Secretary of State certifies that, by reason of the arrangements made for the education of children and young persons employed therein, the exercise and performance of those powers and duties with respect to such children and young persons is unnecessary.