Studies have shown that reading comprehension and vocabulary knowledge are strongly correlated, and researchers have found that word knowledge in primary school can predict how well students will be able to comprehend texts they read in high school. Limited vocabularies prevent students from comprehending a text. Poor readers often read less, because reading is difficult and frustrating for them . This means they don’t read enough to improve their vocabularies, which could, in turn, help them comprehend more. This perpetuating cycle can mean that as students continue through middle school and high school, the gap between good and poor readers grows wider.