Is there an established minimum group size for creating a median growth percentile for a school, disaggregated group, classroom, etc?
Yes – the District and School Growth Summary Reports available here, as well as the Colorado Growth Model, only display medians when data for a minimum of 20 students are available and should be included in this group’s summary median. This is done for two reasons. First, the privacy of individual students must be protected at all times. It is very important not to release data to the public that are not adequately anonymous, and with small numbers of students in a given group, it might be possible to deduce exactly who each person is and what their test scores were. Second, groups that have fewer than 20 members are not fairly characterized by a single number. The data for groups that have fewer than 20 members can be better understood by looking at the complete set of numbers, rather than by attempting to capture them in a single summary statistic. Districts and schools may need to do this as they evaluate their programs and plan for the future, but the general public has no educatio
