The National Quality Framework is used across Australia to drive quality improvement in early childhood settings. Unique to Western Australia, the National Quality Standard is also used in schools to improve quality in classrooms up to Year two (seven to eight years). However, the literature suggests the National Quality Standard is too broad with an emphasis on quantifiable program features (structural quality). As the Classroom Assessment Scoring System (CLASS™) instrument was designed to measure classroom interactions (process quality), the purpose of this current study was to examine its efficacy in Pre-primary (five-year-old) classrooms. A mixed-method research approach was employed to appraise the CLASS instrument as an observational measurement tool for evaluation of quality student and teacher interactions in schools. The quantitative methods involved a statistical analysis of the CLASS instrument ratings and observations and interviews provided a qualitative perspective. Study conclusions suggest that while CLASS offered useful descriptions of quality in Emotional Support and Classroom Organisation, the Instructional Support scores were not consistent with other indicators of quality, and this score was not representative of the instructional quality in some classrooms.