Classroom Assessment Scoring System

The Classroom Assessment Scoring System™ (CLASS™) is an observational instrument developed at the School Center for Advanced Study of Teaching and Learning to assess classroom quality in PK-12 classrooms. It describes multiple dimensions of teaching that are linked to student achievement and development and has been validated in over 2,000 classrooms. The CLASS™ can be used to reliably assess classroom quality for research and program evaluation and also provides a tool to help new and experienced teachers become more effective.

Six versions of CLASS have been developed:

  • Infant
  • Toddler
  • Pre-K
  • K-3
  • Upper Elementary
  • Secondary

The CLASS™ system began as part of a national study in early childhood development. Eventually, that research grew in significance as education policies shifted focus to teacher accountability.

Teachers needed some way to see how their methods were working in the classroom. The CLASS™ instrument became a much-needed tool that could both effectively measure teacher-student interactions in a classroom setting and offer resources for strengthening those interactions across any subject area or age group.

CLASS™ is the only observational teacher-assessment tool that captures teacher behaviors linked to students gains and that has been proven to work in tens of thousands of classrooms, from preschool to high school and beyond.

The CLASS™ tool includes four cycles of 15-minute observations of teachers and students by a certified CLASS™ observer. Those observations are then rated using a manual of behaviors and responses. But it's never been just about measurement. It's about enhancing the overall relationship between teachers and students—and, therefore, the learning. After all, teachers have an influence that can extend beyond a classroom into a lifetime, and that's a role that few in our society have the privilege of playing.

Research conducted in over 6,000 classrooms concludes that from Pre-K programs into the third grade, children in classrooms with higher CLASS™ ratings realize greater gains in achievement and social skill development.

Current work focuses on expanding the CLASS™ into infant and toddler classrooms as well as validation work on Upper Elementary and Secondary versions of CLASS™. CASTL also supports the implementation of CLASS™ as a part of national (Office of Head Start), state (e.g., Virginia, Georgia, Arizona), and local (e.g., San Diego, Cal.) efforts to measure and improve early childhood education.


  • provides programs, schools, and districts with reliable, valid data on teacher effectiveness.
  • creates a common language about effective teaching practices across subject areas and grade levels.
  • helps teachers better understand how their interactions in the classroom affect student learning.
  • documents improvements in the effectiveness of teachers' interactions with students.

For more information about the CLASS™ tools, visit