Findings from several years of participant feedback about the NSF sponsored GK-12 Sensors! program at the University of Maine are described. The program places graduate Fellows in local K-12 classrooms, with the goal of encouraging students to consider science, technology, engineering, and mathematics professions. Three broad themes are discussed: communication, preparation, and "fit." These factors determine the success of GK-12 Fellow placements, as shown by student and teacher evaluations, Fellow satisfaction, and classroom evaluations. Successful placements strengthen program implementation and status in participating schools while marginal placements can negatively affect both teachers and students and erode support for the GK-12 initiative.