Computer simulations are considered efficient in supporting exploratory learning. This paper highlights instruction challenges and undesirable consequences on student learning in exploratory learning with computer simulations in classroom situations. A classroom with students who explore using simulations contains ideas explicated on several communicative channels. We use the professional noticing paradigm to demonstrate how a teacher's ability to listen to students' thinking via a brief encounter in real classroom setups can yield misconstrued interpretation of students' activity and impede learning. We present a case study where a teacher listens to students' thinking in building a model with a dynamic mathematics environment. We show how the teacher's response exacerbated those local confusions in ways that compromised the lesson's goals. We reflect on how the lesson's design influenced these outcomes and survey technology and activity developments to support teachers' noticing.