Despite the growing interest in teaching second language (L2) pragmatics, the issue of assessment of learners' pragmatic skills, particularly in the context of the classroom, seems to be less prominently discussed, even though the assessment is an integral part of the instruction. This qualitative case study aims to demonstrate an operationalization of a principle of pragmatics within the classroom context and demonstrate the effectiveness of teacher-based assessment of pragmatic competence grounded in Vygotsky's sociocultural theory. In freshman English courses at a Japanese university, the teacher researcher implemented pragmatics-focused instruction throughout a semester based on empirically established information on speech acts in English. The instructor used collaboratively developed authentic assessment tools, such as reflective writing, rubrics, role-plays, and self/peer-assessment, and facilitated interaction and assessment in the learning process. These assessments were designed (a) to elicit learners' pragmalinguistic competence to use community norms, (b) to elicit their sociopragmatic awareness of the consequences of their own pragmatic language choice, and (c) to evaluate the extent of the match between learners' intention ("illocution") and interlocutors' interpretation ("perlocution"). Examples of the assessments actually used in the classroom and learner language will be shown, and the instructor's assessment will be interpreted in the sociocultural framework (Vygotsky, 1978). (Contains 2 tables and 5 footnotes.)