In 15 of the 37 states examined—California, Connecticut, North Carolina, Texas, and Virginia, among them—the state bar for proficiency was actually lower than the NAEP threshold for basic.

Science proficiency at each level showed marked gains as well, with a 5.3 percent increase for elementary, 4.5 percent increase for middle-school, and 1.4 percent increase for high-school students.

But proficiency is not the same as grade level, which is a higher bar, Mackey said. “When we think about proficiency,” he said, “those would be students you expect to make A’s or A’s and ...