Once students have a solid understanding of the article and have been able to articulate their responses to it (at least verbally or in shorthand), have them write a letter to Mr. Duncan. After all, they are the products of the American educational system that he says has failed so miserably; they should have a first-hand experience to back up what he says. Have them do the following in their letters:
1. Introduce themselves and explain that they are American high school students.
2. Briefly describe their understanding of the issues raised in the article.
3. Offer opinions on the ideas expressed in the article, and possibly alternative ideas they have about how to improve the quality of American education.
4. Throughout the letter, audience consideration is key to this expository writing lesson. They need to remember that they are writing to an adult who holds a position of authority in our country, and he deserves their respect. Even if they disagree with everything he has said, they will be more persuasive if they write in a respectful tone than they will if they start telling him he's an idiot (I'm sure your students would never consider such a disrespectful thing, would they?). They must demonstrate that they understand his rationale but that they believe there are better ways to solve the problems in American education (unless they agree with him, and then this letter can become fan mail).
Assess their letters for their understanding of the article, their ability to articulate their ideas, and their consideration of their audience. This will also give you a better idea of how well you understand how to teach expository writing.