Formative assessment is about strengthening student learning and can dramatically improve student achievement when it guides changes in day-to-day classroom practice. Any attempt to understand formative assessment must therefore be grounded in a notion of learning, which this paper approaches from a constructivist/experiential perspective. Importantly, for a teacher to genuinely know if a student is learning, the teacher needs to deeply question the learner so as to enter into a student's thinking. Such deep questioning needs to be on going, not one-off single recall questions. This is not something that can be done from the front of the classroom using traditional didactic type approaches or using the initiation-response-feedback-response-feedback (IRFRF) which relates to formative practices. It requires micro-questioning skills on a developmental process, so that such on-going questioning does not degenerate into a sequence of closed interrogative recall questions. Fine-grained analysis of the dialogue used to promote high-level thinking through a questioning scaffold for facilitating formative learning is proposed.