This study uses social network analysis and the classroom observation protocol for undergraduate STEM (COPUS) to characterize six research-based introductory physics curricula. Peer Instruction, Modeling Instruction, ISLE, SCALE-UP, Context-Rich Problems, and Tutorials in Introductory Physics were investigated. Students in each curriculum were given a survey at the beginning and end of term, asking them to self-identify peers with whom they had meaningful interactions in class. Every curriculum showed an increase in the average number of student connections from the beginning of term to the end of term, with the largest increase occurring in Modeling Instruction, SCALE-UP, and Context-Rich Problems. Modeling Instruction was the only curriculum with a drastic change in how tightly connected the student network was. Transitivity increased for all curricula except Peer Instruction. We also spent one week per research site in the middle of the term observing courses using COPUS. From these observations, the student COPUS profiles look nearly the same for Tutorials, ISLE recitations, and Context-Rich Problems discussion sections. This is likely due to the large resolution of activities that can be coded as “other group activity,” suggesting the need for a more detailed observation instrument.