The purpose of this study was twofold. First, to explore middle and high school students' intuitively-based (mis)conceptions in probability, particularly availability and representativeness heuristics. Second, to investigate teachers' awareness of these intuitively-based (mis)conceptions and the effectiveness of their instructional practices to support students' understanding of probability beyond heuristics. The participants were two middle school mathematics teachers, three high school mathematics teachers and their students. Data were collected through a diagnostic test administered to students as a pretest and posttest, interviews with the teachers and two students from each class and classroom observations. The findings indicated the existence of intuitively-based (mis)conceptions regarding availability and representativeness heuristics among middle and high school students. In general, the teachers did not consider the students' intuitions and difficulties in probability in their instructions. Not only did they rarely guide students to analyze and solve the tasks coherently and deliberately, but they also did not discuss students' intuitively-based (mis)conceptions. The results highlighted that if teachers do not attend to student thinking and change their instructional practices accordingly, their knowledge about students' difficulties will not necessarily help students overcome their intuitions and attain a probabilistic way of thinking.