Mobility Rates 2019

The Governor’s Office of Student Achievement (GOSA) publishes mobility rates for Georgia public schools. The GOSA mobility rate, also known as the churn rate, counts the total number of student moves in or out of a school between October 1 and May 1, and divides by the total number of students enrolled on the first Tuesday in October.

The formula is significant because mobility rates can have large variation depending on the formula. The graph below compares the GOSA rate to an alternative rate, labeled the “new student rate”, defined as the percentage of students enrolled on May 1 who started at the school on or after October 1.

Notice the new student mobility rate is usually less than half the GOSA rate. This is because the GOSA rate counts both entries and exits, while the new-student rate only counts entries. Also, if a student moved into and then left a school, the GOSA rate would count that student twice. Both rates are useful, but the new student rate is more helpful context for state-testing results. Because state testing occurs in late April, the new student mobility rate is a close approximation of the percentage of tested students in a school who transferred into the school mid-year.

In analysis we published previously, we found that the relationship between English Language Arts test score growth and mobility was statistically insignificant after controlling for other factors1. However, mobility was associated with a five point decrease in a student’s math student growth percentile. See this post for further details.

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  1. English learner status, direct certification (poverty) and disability status.