By his calculus, students at high-poverty schools that stayed remote for more than half of the 2020-21 school year lost the equivalent of 22 weeks of instruction.

Yet many common interventions do not have enough firepower to make up a gap of that size.

For example, summer school typically brings about five weeks of gain, he estimated. Another popular option, doubling math instruction over an entire school year, may yield a bit more: up to 10 weeks of instructional time.

Even frequent, small group tutoring — considered one of the best, if most expensive, options — cannot single-handedly make up for the worst of the pandemic’s impact. Dr. Kane estimated that when done well over the course of a school year, tutoring may yield the equivalent of about 19 weeks gained.