Professional development to differentiate kindergarten Tier 1 instruction: Can already effective teachers improve student outcomes by differentiating Tier 1 instruction?

Two primary purposes guided this quasi-experimental within-teacher study: (1) to examine changes from baseline through two years of professional development (Individualizing Student Instruction) in kindergarten teachers' differentiation of Tier 1 literacy instruction; (2) to examine changes in reading and vocabulary of three cohorts of the teachers' students (n = 416). Teachers' instruction was observed and students were assessed on standardized measures of vocabulary and word reading. Results suggested that teachers significantly increased their differentiation and students showed significantly greater word reading outcomes relative to baseline. No change was observed for vocabulary. Results have implications for supporting teacher effectiveness through technology-supported professional development.