It seems obvious when you don't need to write things down when you don't feel you have anything to say, but growing up I was always annoyed at how essay-type homework and exams were structured, which values form over substance, because there cannot be much substance when you throw a random topic at a teenage and ask them to care in 90 minutes.

It's much easier to write better essays when you care a lot about something, really want to make it convincing and spend effort polishing your technique based on actual reader feedback. Even the "form" taught at school doesn't really matter because different audiences and topics require different arguments and require you to focus on different details, so the best kinds of essays often look nothing like say full score GRE writing test essays.