Is there a relationship between grammar and reading comprehension? Yes, says Timothy Shanahan on Shanahan on Literacy. In summarizing the research, Shanahan suggests "as students learn to employ more complex sentences in their oral and written language, their ability to make sense of what they read increases, too."
Specific methods for teaching grammar appear to have an effect on comprehension. Strategies that teach sentence combining, a longtime favorite within the special education literature, appears to help students understand what they read, probably because it helps students understand how sentences work. Other research suggests that being familiar with the vocabulary of grammar (noun, adjective) benefits students' understanding.
Shanahan provides a good example of a meaningful way a teacher can "untangle" a complex sentence for students, in hopes that experience with more complex sentences will help them decode them more successfully when they're reading independently. As Shanahan writes, "It is pure romanticism that assumes that children will just figure this kind of thing out without any explicit instruction (and it is even more foolish to assume that English language learners