Teachers' focus on student thinking--and moving beyond superficial "right or wrong" analysis--is essential to effective teaching (Grossman and McDonald 2008; NCTM 2000; Son and Sinclair 2010). Interpreting and evaluating student thinking and providing high-quality feedback are seen as high-leverage practices and are "likely to lead to large advances in student learning" (Ball et al. 2009, p. 461; see also Ball 2001 and TeachingWorks 2013). Creating opportunities for teachers to slow down the feedback process to examine student work and focus explicitly on noticing, interpreting, and providing feedback can improve their practice (van Es and Sherin 2002). The process we describe here is intended as a way to help teachers improve the feedback that they offer to students. The value of teachers working collectively to improve their practice through a more explicit focus on student thinking is well documented (Crespo 2000; Levin, Hammer, and Coffey 2009). The collaborative nature of Internet-based social networks creates opportunities for teachers that transcend both the physical boundaries of schools and districts (Renninger and Shumar 2004; Shumar 2009) and the time constraints of face-to-face environments (Silverman and Clay 2010). In this article, we discuss an online environment designed to support teacher collaboration and enable groups of teachers to become more effective at interpreting and responding to student thinking and student work. The intervention has three primary foci: (a) teacher collaboration around student thinking, (b) developing effective feedback for students, and (c) using technology to mediate and "slow down" these processes while maintaining their authenticity. We share four teachers' participation in the online activities and their claims that this experience changed their daily classroom practice.