There is no wrong or right except that if a student transfers in to a school, and the school does not incur more costs associated with the transfer, that it's wrong that the State should increase revenue to the school.I am sorry but you're mostly wrong.
About the only thing you have right is a school couldn't double their students on the same budget. Your 100 to 200 example.
But most schools could handle a 1% increase on the same budget. Your 100 to 101 example.
There is a lot of info and articles out there about open enrollment. Google some.
You have not successfully refuted my argument. if a school actually benefitted financially by the transfer of a single student, it would also be true that a school would benefit financially from 100 students transferring in. I have demonstrated that this is not true: a school districts students suffer dilution of resources for each and every student that transfers in. The school district does not exist for the benefit of the school district, it exists for the benefit of the students, for which tax money is levied at pain of severe penalty for a property owner refusing to remit. For each student that transfers in, the percentage of revenue available for the education of each existing student is actually diluted.
Also address the fact that teachers are buying classroom supplies in public schools.