Student-centered learning has been shown to be more effective than traditional instructional methods, but deeper investigation is necessary to identify how specific classroom practices lead to improved conceptual learning and student attitudes. The purpose of this study was to identify classroom practices associated with gains in student conceptual understanding and physics identity using pre-post survey data taken from a nationally representative sample of first-semester physics students in four-year colleges and universities. From this sample, we found that students who reported working in small groups during every class saw greater gains in their conceptual understanding of physics than students who did not. Other classroom practices, such as the frequent use of computer simulations, using equipment, and performing labs, were also found to increase student conceptual gains. This work provides further evidence that certain instructional practices--small group learning, in particular--provide benefits to students in college physics classrooms.