In a multi-institutional study, the authors examine elementary preservice teachers' (PSTs') noticing skills before and after their engagement in a mathematics methods course. In particular, the authors examine their use of "Cognitively Guided Instruction" (CGI) as a means of supporting the development of PSTs' "professional noticing of children's mathematical thinking." PSTs (n=123) enrolled in elementary teacher preparation programs across three institutions in the United States were recruited for the study. They were shown a video of four children solving a mathematics problem and asked questions designed to elicit their professional noticing. Analyses revealed that across all three sites the authors' use of CGI supported PSTs in developing two out of the three noticing skills that comprise the professional noticing framework (albeit to differing degrees). Comparing across institutions revealed important implications for (a) the ways in which teacher educators support PSTs' professional noticing and (b) teacher education programs more broadly.