I have a treatment group of size 30 (30 schools in California) that used a math supplemental software. In a simple analysis, I'd like to compare students' average Math growth between our treatment group and a comparable control group. There are many schools in CA that didn't use the software. I'd like the control group to include similar performing schools (their baseline scores be similar to treatment schools with a reasonable margin of error). Also, I'd like the control group sample size be 3 times of my treatment (here 90 schools). There are many many choices of 90 schools out of more than 1000 schools in CA. How would you choose your control group?
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