Within the context of teacher/whole-class instruction sequences, researchers have associated teacher evaluation of pupils' answers to forms of traditional pedagogic discourse, also referred to as "triadic dialogue", "monologic discourse", "recitation" and "Initiation-Response-Evaluation (IRE) sequences". Teacher evaluation has also been associated with pupils' low levels of participation. Explanations and solutions offered by prior research are mainly based on functional categories of actions, characterizing forms and functions of teacher questions and follow-up moves in IRE sequences. Using Conversation Analysis to investigate collections of positive evaluations in video-recorded lessons in two primary school classes, we propose an interactional explanation of the phenomenon and of its predominant use. We show that teachers systematically select the formats of their positive third-turn receipts not only to evaluate pupils' answers for their abstract truth value, but also with respect to the role of each question-answer in the whole activity. We demonstrate that, in this way, teachers convey judgements about the question within the activity; thus, adding a constitutive property to the pedagogic practice and providing students with interpretive resources for a common understanding of pedagogic goals and procedures.