How effective is your school district? A new measure shows where students learn the most

CHICAGO — In the Chicago Public Schools system, enrollment has been declining, the budget is seldom enough, and three in four children come from low-income homes, a profile that would seemingly consign the district to low expectations. But students here appear to be learning faster than those in almost every other school system in the country, according to new data from researchers at Stanford.

The data, based on some 300 million elementary-school test scores across more than 11,000 school districts, tweaks conventional wisdom in many ways. Some urban and Southern districts are doing better than data typically suggests. Some wealthy ones don’t look that effective. Many poor school systems do...