The purpose of this study was to investigate the effects of aligning supplemental reading instruction with core classroom reading instruction on struggling second-grade students’ proficiency in phonics, fluency, vocabulary, and comprehension. Alignment was defined as core classroom and supplemental instruction that are congruent in philosophy, goals, instructional materials, instructional methods, student activities, and reading strategies that follow the same scope and sequence. This study employed a two-group, pre-post true experimental design. Second-grade students (N = 153) scoring in the lowest quartile on the fall Dynamic Indicators of Early Literacy Skills (DIBELS) Oral Reading Fluency assessment were randomly assigned to either an aligned or nonaligned supplemental reading instructional condition received instruction over a 20-week period. Reading specialists in 11 schools provided the supplemental instruction. iv The DIBELS Oral Reading Fluency (ORF) and the Woodcock Reading Mastery-Revised (WRMT-R III) assessments were used to assess student reading growth in phonemic awareness, phonics, fluency, and vocabulary. Each student received one score from the DIBELS ORF and six scores from the WRMT-R III. Seven separate nested analyses of covariance (ANCOVA) were conducted to examine differences in group means at posttest while accounting for nesting of reading specialists within schools. Pretest measures for each of the dependent variables were used as covariates to adjust posttest scores at the end of the study. After controlling for pretest score differences and accounting for the variance associated with reading specialists nested within schools, statistically significant differences were found favoring the aligned supplemental condition for posttest scores on all measures. Effect sizes ranged from small to moderate, with largest effect sizes being found for vocabulary and comprehension. The results of the study suggest that at-risk second-grade students benefitted from supplemental instruction that is aligned to the classroom core reading program.