Through the GK-12 program of the National Science Foundation, graduate student fellows in a coastal marine and wetland studies program were trained to present targeted science concepts to middle- and high-school classes through their own research-based lessons. Initially, they were taught to follow the 5-E learning cycle in lesson plan development, but a streamlined approach targeting the three attributes of science concepts--macroscopic, model, and symbolic--was found to be a better approach, while still incorporating key facets of the 5-E model. Evaluation of the level of inquiry in the classrooms was determined using an inquiry scale from 0 to 4, differentiated by the relative number of actions that are student-centered. The graduate fellows consistently delivered lessons at the targeted levels 2 or 3, guided inquiry. In order to assess student learning, the GK-12 fellows were trained to develop single-item pre- and post-assessments designed to probe middle-level and high-school students' understanding of the macroscopic, model, and symbolic attributes of targeted science concepts. For the lessons based on the research of the fellows, about 80% of the students showed statistically and practically significant learning gains. The GK-12 fellows positively impact the classroom and are effective science ambassadors.