How Did Edbuild Get Arizona’s Per-Student Funding Numbers So Wrong?

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I have a column in the print edition of the Weekly discussing Edbuild’s national study on per student funding. The fact is, Arizona does a reasonably good job of balancing its funding across districts, but Edbuild’s study says Arizona’s funding gap between predominantly white and nonwhite districts is the worst in the country — a $7,613 difference. That figure is wildly wrong.

This post is a short-version review of how badly Edbuild crunched the numbers. We’re going to take a look at a hypothetical school district to see where Edbuild went wrong.

The Gulliver Valley School District is a small district with only two schools, Liliput School and Brobdingnag School. Because Liliput is in a sparsely populated area, it only has 47 students, and it spends $19,700 per student. That sounds like a lot of money, but it costs more to educate a small number of students.

Brobdingnag is in a more populated area. It has 2,425 students. Because of economies of scale, it is able to educate its students for $6,400 per student.

Here’s a math problem. How much does Gulliver Valley District spend per student overall?

Now, you might decide to take the per-student funding number for each school and average the two. If you did, you would say the district spends $13,050 per student.

But that’s not right. You can’t just average the per student cost of two schools when one has 50 times more students than the other. It’s more complicated than that.

If you weight the funding figures for the two schools based on the number of students in each school, you come up with a figure of $6,653 per student for the entire district. That’s the right answer.

Edbuild, for some reason, chose the first, overly simplistic way of arriving at the average per student funding over a number of districts rather than the second. That’s why Edbuild’s numbers are so wrong.

If you want to know more, go to my column in the Weekly.

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