It worked on me
At university my results in advanced mathematics were ordinary. The maths paper for the postgraduate engineering entrance exam was hard, and I prepared for it on my own. Once a week I took the problems I had saved up — the ones I couldn't do — to a tutor, and we stayed on them until I understood every one.
That year one applicant in seven was admitted. Of the eight students the department took, I was the top in mathematics.