Why not grade all schools on growth only?

Most Indiana schools earn A-to-F grades on a formula that gives equal weight to performance and growth on standardized tests. But schools in their first three years of operation – most of which are new charter schools and Indianapolis or Gary “innovation network” schools – can have their grades calculated on growth only, with no consideration of performance. Those schools have an advantage.

As Dylan Peers McCoy of Chalkbeat Indiana pointed out, it means you can’t use the grades to compare schools in a district like IPS. “Of the 11 out of 70 Indianapolis Public Schools campuses that received A marks from the state,” she wrote, “eight were graded based on growth alone.”

So why not grade all schools on growth only, not performance? It seems like that would make a lot of sense. In any given year, schools may not have a lot of control over where their students start out in their math and reading performance. What matters is, do schools help students grow?

One problem is that Indiana’s formula is very generous in awarding points for growth but not for performance. If all schools were graded on growth alone – using the current formula — about 80 percent would get A’s. Conversely, if schools were graded on performance alone, about 2 percent would get A’s.

But we could use growth only and “curve” the scale so fewer schools would get high grades. We could, for example, arbitrarily adjust it to keep the current mix of letter grades, with 27 percent of students getting A’s, 33 percent B’s, 23 percent C’s, 11 percent D’s and 5 percent F’s.

Here is a spreadsheet that shows what “growth grade” each school would get if we did that. They are arranged by school corporation, with charter schools and private schools at the bottom, so you can look up the theoretical growth grade for your local schools. The data are for elementary and middle schools; the grading formula for high schools is more complicated.

You may notice that schools in low-poverty districts still tend to get better grades than schools in high-poverty districts. (If you’re into statistics, the correlation coefficient is plus 0.44). That’s because Indiana measures growth with a “growth to proficiency” system that favors students who have passed state tests.

But if we use growth only, the bias in favor of affluent schools isn’t quite as pervasive as in the state’s current grading system. You’ll find a few schools in wealthy suburban districts that get C’s or D’s and quite a few schools in poor urban or rural districts that get A’s or B’s.

Yes, giving schools letter grades for their performance is a foolish exercise that does a lot more harm than good. But if we’re going to do it, shouldn’t we measure them all with the same yardstick?

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