In this experimental study, 135 preservice teachers developed an instructional plan for a case study within the Multiple Intelligent Mentors Instructing Collaboratively (MIMIC) computer-based environment. Three-dimensional, animated pedagogical agents, representing constructivist and instructivist approaches to instructional planning, served as instructional mentors within the environment and were available to provide advisements. The research design consisted of two factors, (a) instructivist agent (present, absent) and (b) constructivist agent (present, absent), with two primary groups of dependent measures, (a) metacognitive awareness, and (b) attitude. Regarding metacognitive awareness, when the constructivist agent was present, participants tended to report a change in their perspective of instructional planning, reflected less on their thinking, and developed instructional plans rated as more constructivist in underlying pedagogy. Regarding attitude, when the instructivist agent was present, participants reported a more negative disposition regarding instructional planning. Results are discussed in terms of the impact on teaching instructional planning to preservice teachers.