The present study examined the amount, type, and quality of Tier 1 and supplemental reading instruction provided to 4th-grade struggling readers and whether specific elements of instruction predicted growth in reading skills. In all, 110 students identified as having reading difficulty who were receiving school-based reading instruction in 22 classrooms located in 2 states/sites participated. We observed and coded reading instruction for instructional dimensions, including reading components, grouping, and quality. Reading comprehension and vocabulary were the most prevalent components of instruction, whereas limited time was allocated to word-level reading skills. We noted several significant differences in time allocated to overall instruction and components of instruction during Tier 1 between sites. Overall, there were few unique Tier 1 instructional predictors of student achievement at the end of the year. Students receiving supplemental reading instruction outperformed those students receiving only Tier 1 on measures of oral reading fluency. We discuss implications for instruction and future research.