Sounds easy.

But, that "free money" is a state determined amount that turns out to be considerably less than what some districts spend on a per pupil basis. It doesn't make sense for a district to accept $6000 from the state to provide an education to a student that costs $8000.

Most schools know exactly what it costs to educate one student. The question generally is can we add one more without requiring more space (another classroom) or additional teachers ( more labor cost). Right now most schools are not at 100% of design capacity.

1 extra student is merely hundreds of dollars in actual net expenses and the acceptance of such a student will drive down the average cost not increase it, in most cases. Example school A has 100 students in grade 3 with 5 classrooms and 5 teachers. Classroom capacity is 25 per classroom. If all expenses added together for energy, building, materials ,labor etc. is $7,000 per student, you then know that the brake even point for grade 3 at this school is $700,000. There are 25 spots available for new students ( 25 design maximum -20 current enrolled =5 per classroom ×5 classrooms =25.). If my materials cost for each student is $200 / year ( books, depreciation for desk, etc) and the state is giving $6,000 per transfer student the school nets a $5,800 margin ($6,000 -$200=$5800) for each additional student they bring in even though the total gross recieved is less than the AVERAGE COST PER STUDENT. So if school A brings in 10 additional students raising each classroom to 22 students they simultaneously net an additional $58,000. This additional money will then demonstrate $6,000 received for each of the 10 new students when the average was $7,000 / student will actually make the new average drop to $6,381.82 per student ( $700,00 + $58,000 = $758,000 ÷ 110 students = $6,381.82)

I know it seems counter intuitive.