Each principal of a school of one to four classrooms shall be paid in addition to salary according to scale, Article 5.09, an allowance of $1444 per full time teacher with pro-rated allowances for less than full time teachers assigned to his/her school, less the approved administrative time for that principal. Effective September 2015, the allowance shall increase to $1473. Effective September 2016, the allowance shall increase to $1503. Effective September 2017, the allowance shall increase to $1525. Effective January 2018, the allowance shall increase to $1548.