The purpose of this study was to examine the effects of diagnostic formative assessment feedback on early literacy skills. The participants were 12 first-grade general education teachers and 51 of their students who were assigned to the following treatments, diagnostic feedback and skills feedback (control) which lasted for 10 weeks. During the study, participating teachers in both feedback conditions reviewed student response patterns on a one-minute assessment of word decoding to identify their students’ phase of word reading development. Teachers of students in the diagnostic feedback condition were also provided instructional recommendations aligned to student word reading needs. Three measures were collected in the course of the study. First, all students were measured on word decoding for a total of four data waves. Second, teachers in both conditions recorded the number of instructional changes they planned to implement in response to changing student data. Third, a measure of oral reading fluency was collected at posttest. A multilevel growth-curve model indicated diagnostic feedback was a non-significant predictor of decoding skills. Analysis of covariance indicated diagnostic feedback group affiliation was not associated with oral reading fluency scores after controlling for initial decoding skills. With regards to instructional planning, skills feedback teachers reported a higher number of instructional changes. In addition, skills feedback teachers viewed progress monitoring feedback as significantly more helpful for planning compared to diagnostic teachers. Amount of instructional changes was unrelated to posttest decoding and oral reading fluency scores. Implications for practice and suggestions for future research will be discussed.