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.