It’s no secret that many Americans are lousy writers. Just ask any college professor or employer, including those at prestigious institutions. With the advent of email, writing ability has become more important than ever, and writing deficiencies have become increasingly apparent.

Surely one reason so many Americans lack writing skills is that, for decades, most U.S. schools haven’t taught them. In 2011, a nationwide test found that only 24 percent of students in eighth and 12th grades were proficient in writing, and just 3 percent were advanced.

If students get writing assignments at all, they’re usually of the “write about how you feel” variety. There’s value to that kind of exercise, but it doesn’t provide kids with the tools they need to write analytically.

The Common Core education standards, adopted by more than 40 states and the District of Columbia, attempt to address this deficit. They require that students learn to write fluently about the meaning of what they’re learning — not just in English class, but also in history, science and maybe even math class.

That makes sense: When students put what they’ve read into their own words, they’re more likely to absorb and retain it. And learning to write clearly requires learning to think clearly.

But the authors of the Common Core focused just on the skills that students should have at each grade level, not on how to impart them. And few teachers have been trained to teach these writing skills, apparently because educators believe that students will just pick them up through reading. Obviously, most don’t.

The standards also assume students in middle and high school already know the rules of capitalization, punctuation and sentence construction. But that’s often not the case, especially in high-poverty environments.

Faced with high school seniors who can’t compose a simple sentence, teachers may throw up their hands when confronted with an English language arts standard saying their students should “use appropriate and varied transitions and syntax to link the major sections of the text, create cohesion, and clarify the relationships among complex ideas and concepts.”

You have to learn to add before you can do calculus. Similarly, before students can write a coherent five-paragraph essay, they need to learn to write a decent sentence — no matter what grade they’re in.

That doesn’t mean teachers should drill students on grammar rules, an approach that research has shown doesn’t actually work. Instead, they can ask students to decide whether a group of words is a sentence or a fragment — not an easy distinction for many to grasp.

Once students understand the concept of a sentence, they can learn to use conjunctions such as “but” and “because.” Then they can create complex sentences — including those beginning with subordinating conjunctions such as “although” or “despite” — to introduce variety into their writing. Generally, students need to learn how people write as opposed to how they speak.

When students have a basic grasp of sentences, then — and only then — should they move on to planning and drafting paragraphs. Once they can write paragraphs, they can tackle essays.

The Common Core’s failure to acknowledge that many older students lack basic writing skills can have counterproductive results. For example, the Education Trust recently studied more than 1,200 middle school writing assignments to see whether they aligned with the Common Core and faulted them in part because they didn’t require students to write at length.

“In grades six to eight, we must see extended writing — multiple cohesive paragraphs that clearly reflect strong organization and style,” the report’s authors lamented.

But if middle and high school students are writing poorly constructed sentences, they’ll almost certainly end up writing poorly constructed essays. And while the Common Core demands that students engage in critical thinking, sentence-length assignments can fulfill that mandate as well as longer ones.

For example, a teacher can give students the beginning of a sentence based on a text and ask them to finish it using the conjunction “but,” requiring them to examine the text closely enough to find two contrasting ideas. That gives the teacher a manageable opportunity not only to correct writing mistakes, but also to uncover what students haven’t understood. A teacher confronted with an essay full of mechanical and conceptual errors may not know where to begin in correcting the essay.

It’s understandable that educators and policymakers feel a sense of urgency about getting students to write at length in the upper grades. But if we keep expecting students who can’t construct decent sentences to magically produce coherent essays, we’ll remain a nation of lousy writers forever.

Natalie Wexler is chairwomanfor the board of trustees for the Writing Revolution.