This document provides a summary of research on the causes of struggling readers. It discusses four main theories: cultural mismatch theories, deprivation theories, difference theories, and normative theories. Cultural mismatch theories suggest that students who lack experiences matching school expectations for reading may struggle. Deprivation theories indicate struggles may stem from cognitive processing problems. Difference theories posit potential struggles could be due to inappropriate or unresponsive instruction. Normative theories argue some students are labeled as struggling simply due to a need to identify successful readers against a norm. The document explores applying these theories to understand individual struggling readers.