‘ 4. Grants; contingent extension of full implementation. During the period of transition to proficiency-based graduation in accordance with this section, the department, if funds are available, shall make annual transition grants to each school administrative unit equal to 1/10 of 1% of the school administrative unit's total cost of education calculated under section 15688, subsection 1 to be used in the manner determined by the school administrative unit to fund the costs of the transition not otherwise subsidized by the State. The date for implementation of the awarding of diplomas based on student demonstration of proficiency as described in this section is extended one year for each year for which transition grants are not made available to a school administrative unit or for which levels of general purpose aid for local schools fall below school year 2012-2013 levels.’