Before any school district builds new facilities, it should conduct a demographic study so that it has a reasonably accurate picture of the number of students who are going to be in the schools during the next five and 10 years, and of the overall trend (is the district growing or declining?).

For most districts, a simple“cohort survival” study will do. Cohort survival suggests that under normal circumstances, the percentage of children who have advanced from one grade to the next during the last three to five years (cohort survival) will continue during the next three to five years. Unless significant outside changes are taking place affecting the district (a housing boom, closing of a non-public school, significant job loss, etc.), that’s a pretty good assumption. But sometimes more subtle changes occur within a district. One of those may be a change in the ethnicity of families and students.

George and Eunice Grier have been carrying out demographic projections for the New York City schools for more than a decade. During that time, they have been extraordinarily accurate in projecting a changing student population. The key to their success has been the use of ethnic projections, a concept that they pioneered. Effectively, the Griers divide students into groups defined by their ethnicity and project each separately, assuming that different economic and cultural groups might have a different impact on the schools.

Given the size of New York City and the size of the ethnic groups, it was easy to understand how projecting each separately might provide better overall projections. But could the same techniques be used in smaller districts? And, if ethnic projections were made, would there be any significant difference?

A year ago, the Griers and I were working together projecting the likely student population for a mid-sized school district with about 15,000 students. The district had been growing for the last four years and there was information indicating that it was going to grow some more. The cohort survival projection numbers did not agree. They showed student population flattening. The Griers suggested we make use of ethnic data to project each group separately.

Using ethnic projections, we discovered that the (majority) white population was declining, but two ethnic groups — Blacks and Hispanics — were growing. When we had looked at the district as a whole, the projections had been skewed downward by the fact that the majority group was declining. When we projected each group individually, it became clear that the minority populations were growing faster than the majority was declining. Overall student population would increase.

Recently, I was helping a very small district (1,200 total students) project its future student population. Once again, though the number of students enrolled had been increasing during the last three years, projections of the future showed enrollment declining.

Examination of the data revealed the cause — births during the last few years had declined, so smaller classes were expected. When I examined enrollment trends after dividing student population by ethnicity, I uncovered a very different and interesting picture. In this case, members of a single ethnic group had recently moved to the district. Many of the new families came with children of school age. Births during the last five years were largely to members of the white majority, but minority students were bulking up the middle grades in the elementary schools and the middle and high school. The ethnic projections showed that overall population is likely to increase during the next decade.

If your district has a diverse student population, you may find that projecting students by ethnicity can provide more accurate estimates. Such an analysis can also reveal some underlying trends that may be important to the future. For many years in the small district we studied, students had entered the district at the sixth and ninth grades as they aged out of area non-public schools. That influx is slowing, possibly the first evidence of white parents wondering whether to send their children to the district’s schools. If that is true, the district has an early warning and an opportunity to take steps to meet a potential problem before it becomes a major issue.