A study was initiated at the inception of the Exploring the Environment (ETE) project to look at critical factors concerning the use of problem-based learning in Earth science classes. During the 1995-96 school year, the Tropical Poison module from the ETE Project was evaluated in nine high schools across the country. The module introduced students to authentic environmental issues within the context of an ill-structured problem. The ETE Project Team also conducted one-week workshops for participating teachers-with five of the nine teachers participating in this study attending the workshop. An "ex post facto," causal-comparative research design was used. Likert data from teacher and student surveys, and end-of-exercise reports written by students were analyzed to seek out causes, relationships, and their meanings. Research questions addressed student attitudes toward the understanding of the problem solving process and their perception of their involvement in learning in an inquiry environment. The data were analyzed comparing students' scores by teachers who participated in the week-long workshop, versus those who did not. Students whose teachers had attended a week of professional development prior to this study, had significantly higher attitude scores concerning problem solving and engagement. The same students also had significantly better end-of-module written reports than the students of teachers who did not attend the ETE summer workshop. Though not an experimental design, and the subjects varied as to background and pre-knowledge, this brief study supports the importance of providing professional development for teachers devoted to using inquiry-based methods in science classrooms. Blind Review Form is appended. (Contains 13 references.) (Author/YDS)