Preservice undergraduates should acquire many skills in their teacher preparation program that support them as future effective teachers. For special education preservice teachers, one of these important skills is teaching with the constant time delay procedure, an evidence-based practice for teaching learners with moderate or severe disabilities. In this study, participants first learned to use the constant time delay procedure in class and then practiced the procedure either with an avatar in a mixed-reality environment (experimental group) or with a peer in a classroom role play activity (control group). Participants then used the procedure to teach vocabulary words to a learner. A pre-experimental group design was used to compare the fidelity of implementation of the procedure for both groups. A paired t-test compared the number of correct constant time delay trials implemented for participants in both groups and found no significant difference between types of experience (mixed-reality or role play) and correct use of the procedure. Implications for practice include a discussion of what additional instructional supports preservice undergraduates might need to implement the constant time delay procedure with fidelity.