There exist both explicit and implicit approaches to teaching students how to solve physics problems involving multiple representations. In the former, students are taught explicit problem-solving approaches, such as lists of steps, and these approaches are emphasized throughout the course. In the latter, good problem-solving strategies are modeled for students by the instructor and homework and exams present problems that require multiple representation use, but students are rarely told explicitly to take a given approach. We report on comparative study of these two approaches; students at Rutgers University receive explicit instruction, while students from the University of Colorado receive implicit instruction. Students in each course solve five common electrostatics problems of varying difficulty. We compare student performances and their use of pictures and free-body diagrams. We also compare the instructional environments, looking at teaching approaches and the frequency of multiple-representation use in lectures and exams. We find that students learning via implicit instruction do slightly better and use multiple representations more often on the shorter problems, but that students learning via explicit instruction are more likely to generate correct free-body diagrams on the hardest problem.