Never for my own benefit. I’ve always been a good test-taker.
However, my Sophomore year of high school I had a teacher who was universally disliked. The boys disliked him because he was a chauvanist and gave the girls better grades. The girls disliked him because he was a chauvanist who gave the girls who wore low cut blouses and suffered his comments on their necklaces the best grades.
One day he was out, and we had a substitute. The sub was my Dungeon Master (her daughter was a friend of mine, and we all played D&D together). The test was Latin roots of English words. I can’t remember what the exact circumstances were, but for some reason none of us knew what was going on—the material had just not been taught.
I was pulling my third year of straight As in Spanish class, and between my own knowledge of etymology and what I could remember from Spanish, I managed to get the answers worked out. Probably more than half the class benefited from my work.
It stopped the bullying for a week or so, which was a welcome respite.