Certificated Leave Replacement – “Differential” Pay and Use of Temporary Employees (K-12)

The following question has been recently posed by several of our school district clients regarding “differential” pay to permanent certificated employees:, If a school district decides to hire a temporary employee instead of a substitute when a permanent certificated employee is out on a long-term leave, can the district deduct the temporary employee’s salary from the salary of the permanent employee on leave or are they limited to only deducting the daily substitute rate?