On or before the first day of July of every year, the board of revision of taxes of counties of the first class, the board of property assessment appeals and review of counties of the second class, the board for the assessment and revision of taxes of counties of the third class, and the county commissioners of all other counties, shall file a certificate with the Superintendent of Public Instruction,¹ in such form as he may prescribe and on blanks to be furnished by him, showing the assessed valuation of all real property in each school district in the county on which the taxes for the then current year are levied.