Our research framework includes a taxonomy of que stions and a conceptual-exploration proce ss model based on dialogue acts. We report preliminary results of research employing the dialogue acts as a coding scheme to model and measure design-team processes related to generating design alternatives and making decisions. The results support the tentative conclusion that team performance on a conceptual design task is positively correlated with the frequency of a dialogue act we call "limit-handling." Remaining challenges include establishing higher reliability of the coding scheme, more fully integrating and validating prior models, and validating dialogue facilitation techniques to support conceptual design, decision analysis and risk analysis.