In response to growing interest in mindfulness as a support for educators, the current study sought to create and test a new multidimensional and multi-informant measure of teacher mindfulness in the classroom. To counter some of the limitations of context-general self-reports, we designed two theoretically based classroom-specific measures that capture the experience and expression of mindful teacher behavior from the perspective of "teachers" and "students". Drawing on emerging consensus from experts on mindfulness in education, the measures incorporated three dimensions of mindfulness, namely, Calm, Clear, and Kind teacher behavior in the classroom, as well as their antitheses, namely, Reactive, Distracted, and Critical teacher behavior. Utilizing data from 78 sixth- to eighth-grade teachers and 550 of their students, teacher- and student-report item sets tapping these dimensions were tested for reliability and validity across three time points. Based on confirmatory factor, reliability, structural invariance, and correlational analyses, subscales generally demonstrated satisfactory psychometric properties, cross-year stabilities, convergent and criterion validity with multiple established measures, and some overlap across reporters. In terms of connections to observer ratings from the CLASS-S, teacher subscales showed consistent but modest connections, whereas student subscales showed higher correlations (especially at time 2), suggesting that students and observers converged in their perceptions of teachers' "expressions" of mindfulness. Possible improvements to both measures as well as implications for future research on teacher mindfulness are discussed.