Although coaching is a popular approach for enhancing the quality of Tier 1 instruction, limited research has addressed observational measures specifically designed to focus coaching on evidence-based practices. This study explains the development of the prekindergarten (pre-k) Classroom Observation Tool (COT) designed for use in a data-based coaching model. We examined psychometric characteristics of the COT and explored how coaches and teachers used the COT goal-setting system. The study included 193 coaches working with 3,909 pre-k teachers in a statewide professional development program. Classrooms served 3 and 4 year olds (n = 56,390) enrolled mostly in Title I, Head Start, and other need-based pre-k programs. Coaches used the COT during a 2-hr observation at the beginning of the academic year. Teachers collected progress-monitoring data on children's language, literacy, and math outcomes three times during the year. Results indicated a theoretically supported eight-factor structure of the COT across language, literacy, and math instructional domains. Overall interrater reliability among coaches was good (.75). Although correlations with an established teacher observation measure were small, significant positive relations between COT scores and children's literacy outcomes indicate promising predictive validity. Patterns of goal-setting behaviors indicate teachers and coaches set an average of 43.17 goals during the academic year, and coaches reported that 80.62% of goals were met. Both coaches and teachers reported the COT was a helpful measure for enhancing quality of Tier 1 instruction. Limitations of the current study and implications for research and data-based coaching efforts are discussed.