It's a reasonable hypothesis that struggling students mainly need better study skills — and a well-designed controlled comparison found that skills instruction alone, however attentive and well-delivered, produced no measurable improvement compared to a workshop that instead taught students that intelligence itself could be developed through effort. The growth-mindset group's improvement wasn't explained by receiving better tactics; it was explained by a shift in whether effort felt worth investing in at all.
What makes this finding especially strong as evidence is the blind evaluation built into it: teachers who didn't know which students had attended which workshop still independently noticed and reported differences in motivation between the two groups, ruling out the possibility that the effect was just teachers' expectations shaping their own grading.
Researchers ran a workshop teaching struggling students that intelligence could be developed through effort, and compared it against a parallel workshop offering equally attentive study-skills tutoring but no belief-change component. Teachers who didn't know which students had attended which workshop nonetheless singled out students from the growth-mindset workshop as showing noticeably improved motivation over the course of the semester. By semester's end, the growth-mindset group showed real, measurable gains in math grades, while the study-skills-only group — despite receiving equally attentive tutoring — showed essentially none.