Despite the growing number of collaborations between volunteers and professional scientists, research efforts investigating the impacts of such collaborations, which we have termed Public Participation in Scientific Research (PPSR), have been very limited. Examples of PPSR projects include citizen science, volunteer monitoring, and participatory action research. In this report conducted under the auspices of CAISE (Center for the Advancement of Informal Science Education), we present a conceptual model consisting of three permeable categories of PPSR, distinguished primarily by the level of decision-making control of participants in the scientific process. To analyze outcomes we examined case studies of each type of project using a rubric based on the Evaluation Framework for Informal Science Education. Our findings suggest that the level of participant decision-making control may impact participant outcomes differently. We conclude with specific recommendations to further advance our understanding and practice of environmental education through public participation in scientific research. An appendix presents: Public Participation in Research Projects funded by the National Science Foundation since 2000. (Contains 5 tables and 2 footnotes.) [This report was published by the Center for Advancement of Informal Science Education (CAISE).]