Apply grade 4 Reading standards to informational texts (e.g., "Explain how an author uses reasons and evidence to support particular points in a text").

This is the kissing cousin to W.4.9.A, with an informational text twist. So if your students are to "explain how an author uses reasons and evidence to support particular points in a text," you'll have them write their explanation. It's just like showing your work in Math class, except you're in English class.