This study aims to investigate the broader impacts of student-scientist partnership with an emphasis on scientists' possible contributions to students' understanding and proficiencies of science. Appeals from the National Science Foundation have specifically called for broader participation and direct involvement in science and the enhancement of research and education through the linking of scientists with other programs. The Botanical Society of America's PlantingScience project is a partnership of students, science teachers, and scientist-mentors working together in authentic science learning. This dissertation includes three papers. The first paper is an extensive literature review focusing on how scientists can contribute to students' science learning via online mentoring. The second paper applies a grounded theory approach to build a theory that explains how scientists talk about science when they engage in inquiry activities with students and how this interaction occurs. The third study, which is a mixed methods study, investigates how scientists contribute to students' science proficiencies and what kind of patterns exist between scientist-mentors and student-teams during inquiry engagement. The literature review reveals an information gap exploring how scientists reflect their understanding of science to K-12 students when they work together in a partnership model. This review pointed out three main questions regarding student-scientist partnerships via online mentoring: (1) What do scientists say about science when they engage in online dialogue about students' inquiry projects? (2) What are the connections between scientists' demographics, the subject of the inquiry, and the way they explain the nature of science? and (3) What is the relationship between the quality of students' inquiries and what their mentors reveal about the nature of science in their dialogues? The results of the grounded theory study revealed the educational, social, and cultural means of the interaction between two parties-- students and scientists. Also, investigation of various cases allowed a better understanding of the essence of nature and culture of science from practitioners' perspectives. Finally, the mixed methods study revealed that scientists contributed to the authenticity of students' inquiry experiences by encouraging them to understand scientific explanations, generate scientific evidence with them, reflect on scientific knowledge, and participate productively in scientific discussions. The electronic version of this dissertation is accessible from http://hdl.handle.net/1969.1/155639