The review analyzed evidence from 205 studies, 186 of which were randomized controlled trials, to examine the effects of targeted school-based interventions on students' performance on standardized tests in reading and math.

Peer-assisted instruction and small-group instruction by adults were among the most effective interventions. The authors noted that these have substantial potential to boost skills in students experiencing academic difficulties.

"It is exciting to see that there are many interventions with substantial impacts on math and reading skills, especially in these times when many students have not been able to attend school and the number of students who need extra help may be even larger than usual," said lead author Jens Dietrichson, PhD, of VIVE, the Danish Center for Social Science Research. "It is also interesting that there is large variation: far from all interventions have positive effects, and there are substantial and robust differences between the types of interventions. Thus, schools can boost the skills of students with difficulties by implementing targeted interventions, but it matters greatly how they do it."