This study explored the nature of the relationship between a fifth-grade teacher and an informal science educator as they planned and implemented a life science unit in the classroom, and sought to define this relationship in order to gain insight into the roles of each educator. In addition, student learning as a result of instruction was assessed. Prior research has predominately examined relationships and roles of groups of teachers and informal educators in the museum setting (Tal et al. in "Sci Educ" 89:920-935, 2005; Tal and Steiner in "Can J Sci Math Technol Educ" 6:25-46, 2006; Tran 2007). The current study utilized case study methodology to examine one relationship (between two educators) in more depth and in a different setting--an elementary classroom. The relationship was defined through a framework of cooperation, coordination, and collaboration (Buck 1998; "Intriligator" 1986, 1992) containing eight dimensions. Findings suggest a relationship of coordination, which requires moderate commitment, risk, negotiation, and involvement, and examined the roles that each educator played and how they negotiated these roles. Consistent with previous examinations in science education of educator roles, the informal educator's role was to provide the students with expertise and resources not readily available to them. The roles played by the classroom teacher included classroom management, making connections to classroom activities and curricula, and clarifying concepts. Both educators' perceptions suggested they were at ease with their roles and that they felt these roles were critical to the optimization of the short time frames (1 h) the informal educator was in the classroom. Pre and posttest tests demonstrated students learned as a result of the programs.