Section 12C. There shall be established upon the books of the commonwealth a separate fund, to be known as the School Choice Tuition Trust Fund. The state treasurer shall deposit in such fund all school choice tuition amounts deducted from education aid of sending districts, all amounts deducted from other aid to cities and towns, and amounts appropriated due to an excess of deductions over such other aid, as such terms and amounts are defined in section twelve B. Monies in the fund shall be disbursed, without further appropriation, by the treasurer to receiving districts as such districts’ school choice tuition amounts due such receiving districts, as such terms and amounts are defined in section twelve B.