A certificate permitting the employment of a minor during the school term, but not during the daily period of the school session, may be granted if such minor maintains a passing grade in all studies pursued by the minor in such school. No minor may be employed who at the time is guilty of truancy or of deficiency in studies, as determined by the minor’s parent or guardian, or the principal of the school which the minor attends, or a principal in the municipality in which the minor resides, or the labor commissioner or the commissioner’s agent or representative.