I made no indication I was disagreeing with OP. I would like to reply to your points and elaborate. I think your standards for high school writing are too high

I made no indication I was disagreeing with OP. I would like to reply to your points and elaborate. I think your standards for high school writing are too high. "Clear, complete" sounds more like graduate-level work. Try reading papers from an undergraduate writing class sometime--the basic expectation is that students present a clear thesis with arguments that support it. The thesis itself can be wrong, reflect a facile understanding of the topic, have well-known rebuttals, etc. High-school writing is graded superficially for good and bad reasons. Let's get bad reasons out of the way first--teachers are overworked and underpaid, and don't have enough time to do a better job because they are busy with administrative bullshit or standardized tests. There are good reasons--superficial problems often reflect a lack of understanding for how ideas connect to one another. The correct use of paragraphs means understanding whether sentences express related ideas. If you can't tell if two ideas are related, you can't make paragraphs. Coordinating conjuctions like "and" or "but" have the same grammatical function but express different relationships between the clauses. Students use the wrong one, and it's often because they haven't thought about whether two ideas contrast with each other. Spot the "superficial" problems and you find markers for problems with the underlying ideas. If you don't assign essays to high school students, you're lowering the bar across the board, and I think we would end up with a crisis in graduate schools. High school is not just a fact / skill dump for various bits of subject matter like history and mathematics or whatever you want to include in the curriculum. It's also a place where people develop some of their critical thinking skills. Writing bad essays is a step along that path.