The field of science education has put effort into providing opportunities for students to position themselves as epistemic agents pursuing the goal of making sense of natural phenomena. However, students often struggle in adapting scientific practices to achieve the sense-making goal. In this position paper, we conceptualise students' difficulties in understanding and adapting scientific practices in the science classroom by using the concept of "threshold practices." Based on literature related to threshold practices and two cases that demonstrate students' learning of threshold practices, we discuss four features of threshold practices: (1) Troublesome: Threshold practices are unfamiliar to students and thus challenging for them to adapt; (2) Transformative: Learning threshold practices facilitates transformations in students' engagement in practices as well as their identities into epistemic agents; (3) Integrative: Performing an activity in a threshold practice enables students to carry out other interrelated activities; and (4) Disciplinarily bounded: A threshold practice is bounded to a particular discipline. Teachers noticing students' threshold practices, providing resources to overcome the thresholds, and encouraging students' reflection on their practices are suggested as teaching considerations to support students' adaptation of scientific practices.