This study examined the effects of a Partnering workshop on construction personnel's attitudes and perceptions. The subjects included Iowa Department of Transportation personnel and independent contractors in the state of Iowa. A two-day Partnering workshop conducted prior to the start of six heavy highway construction projects served as the treatment. The sample included 261 subjects: 146 participated in the treatment, 90 worked with the participants on Partnering projects but did not participate in the treatment themselves. Twenty-five subjects worked on a non-Partnering control project;The dependent variables were problem solving, teamwork, communication, trust, respect and workmanship. A 41-item and 20-item questionnaire were used to assess these variables. The treatment participants were asked to assess their own attitudes and perceptions on previous non-Partnering projects. The same was asked of them following the Partnering workshop. The findings reveal that the treatment participants' perceptions and attitudes of the variables under study were significantly (p ≤.05) more positive as reported for Partnering projects than reported for non-Partnering projects. However, those subjects who did not participate in the treatment did not perceive improvements. This suggests that the effects of the treatment did not transfer from participant to non-participant;Quality, profitability and productivity were also included as dependent variables and were assessed through a separate instrument based on data independent of perceptions. The productivity of the Partnering projects were significantly (p ≤.05) higher than non-Partnering projects. No significant (p ≤.05) increases in quality or profitability were found for the Partnering projects;The findings of this study support many of the claims stated in the Partnering literature. Additional research as necessary, however, as many questions are still unanswered. This paper offers recommendations for future research.