This study explores the diffusion of Web 2.0 technologies among science educators and the ways that these technologies are used to build teacher professional communities of practice (CoP) in life sciences and physical sciences. We used surveys and web analytics collected over a 21-month period to examine factors that motivate teachers to collaborate in these CoPs and the extent to which collaborative participation contributes to the development of sociotechnical capital and job outcomes, such as instructional practices and self-efficacy for science instruction. Results showed that only the lack of co-located peers at teachers' schools predicted CoP participation. Participation did not predict job outcomes, but it did predict some aspects of sociotechnical capital, such as a cohesive climate and situated knowledge. In addition, sociotechnical capital was associated with job outcomes, including use of inquiry-based instruction, use of inquiry-based classroom activities and teacher self-efficacy. The lack of effect of most of the antecedent variables in predicting participation and the relatively minor role of participation in contributing to sociotechnical capital and job outcomes may be explained by floor effects on participation due to infrequent and ephemeral engagement of CoP members. Although participation rates were generally low, the positive association of participation with sociotechnical capital as well as generally favorable ratings of sociotechnical constructs suggest that online CoPs may have value for distributed science educators. Future research should address whether persistent participation by individuals is needed to build and sustain sociotechnical capital in online CoPs and to enhance development of participants' teaching attitudes/practices.