Pay attention in class, especially science class, because you will need the information later in the episode.
This trope is the awkward tendency of programs to use precisely what they learned in school (almost always science) earlier that episode, and to lampshade it through grating dialogue. Shows aimed at an older audience can make it slightly more subtle; even so, it usually comes out like this:
"Oh yes, I totally forgot. How conveniently stupid of me!"
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- The Dethklok song "Bloodrocuted" has the protagonist come up with the idea of using his own blood to electrocute his pursuers after having a brief flashback to his high school biology class, where he learned that blood conducts electricity.
- Katawa Shoujo has this in Emi's route. Mutou, Yamaku's science teacher, takes Hisao aside for a short lecture about observing things (if you let him). Namely, that if you can't observe something directly, observe its effect on other things. This advice comes in very handy, as it unlocks new dialogue options when Hisao and Emi's relationship starts getting off-track.