The number of poor students enrolled in a certain school district is one of the most important education data points that exists, and the stakes are high for getting the count right. But counting how many students qualify for free and reduced-priced lunch is no longer a reliable proxy for poverty. And getting an accurate count is becoming more difficult in part due to increasing numbers of students in the country illegally and students from immigrant families, both of whom are wary of enrolling in government benefit programs.