This study described the conceptual understandings of 50 early childhood (Pre-K-3) preservice teachers about standards-based lunar concepts before and after inquiry-based instruction utilizing educational technology. The instructional intervention integrated the planetarium software "Starry Night Backyard[TM]" with instruction on moon phases from "Physics by Inquiry" by McDermott (1996). Data sources included drawings, interviews, and a lunar shapes card sort. Videotapes of participants' interviews were used along with the drawings and card sorting responses during data analysis. The various data were analyzed via a constant comparative method in order to produce profiles of each participant's pre- and postinstruction conceptual understandings of moon phases. Results indicated that before instruction none of the participants understood the cause of moon phases, and none were able to draw both scientific moon shapes and sequences. After the instruction with technology integration, most participants (82%) held a scientific understanding of the cause of moon phases and were able to draw scientific shapes and sequences (80%). The results of this study demonstrate that a well-designed computer simulation used within a conceptual change model of instruction can be very effective in promoting scientific understandings. (Contains 4 figures and 8 tables.)