In this exploratory study, 135 pre-service teachers developed an instructional plan for a case study within the MIMIC (Multiple Intelligent Mentors Instructing Collaboratively) computer-based environment. Three-dimensional, animated pedagogical computer agents, representing constructivist and instructivist approaches to instructional planning, served as instructional mentors within the environment and were available to provide suggestions. The research design was comprised of two two-factor MANOVAs with the instructivist agent (present, absent) and constructivist agent (present, absent) serving as the two factors, with two groups of dependent measures: awareness and attitude. Additionally, the value of the agents and overall differences between high and low performers were investigated. Regarding awareness, main effects for the presence of the constructivist agent indicated that 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, a main effect for the presence of the instructivist agent indicated that 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 pre-service teachers. (Contains 35 references.) (Author/AEF)