Hispanic literacy development in the Southwestern US is examined through standardized assessment data derived from recent National Assessment of Educational Progress (NAEP) and Texas Academic Performance Reports (TAPR). This longitudinal study focuses on significant variables across a spectrum of grade levels for Hispanics of Mexican descent. Results confirm a steady decline in reading performance after 4th grade. At the secondary level, a corresponding "Matthew effect" is also detected--whereby students whose reading development begins to decline in 4th grade continues to decline in secondary grades. Socioeconomic status (SES), gender, and bilingual language development are correlated as mitigating factors for reading performance. Hispanic students who attended a slightly more affluent and racially diverse high school showed moderately better reading scores. Hispanic males with low SES should be seen as most at-risk for reading failure in this region. Recommendations for alleviating these developmental literacy challenges include a more systematic implementation of "Science of Teaching Reading" (STR) at the earlier grade levels and raising awareness about gender differences in reading instruction. Parents, educators, and administrators interested in Hispanic reading development should find this study informative.