This study examines patterns in how a group of fifth- and sixth-grade teachers evaluated and reported using different types of curriculum resources to support their teaching in relation to the mathematical concepts outlined in the Common Core State Standards for Mathematics. In particular, it explores the use of resources that were available to teachers through the Internet, including the extent to which they used these resources to supplement their district-provided materials and the criteria they used to evaluate specific web-based resources. Data were collected through the use of implementation logs and video recordings of professional development sessions related to curricular resources. The results of the study show that resource use varied widely from teacher to teacher, but also that Internet resources were often used as much as, or more than, other resources like textbooks. When evaluating specific resources, the teachers referred to a variety of criteria, but did not often coordinate multiple criteria when making evaluations. Also, they tended to positively evaluate most resources; negative evaluations were primarily given for resources that teachers believed students would be unable to complete successfully. We use these results to build on the idea of curricular reasoning (Roth McDuffie & Mather, 2009), and suggest that teachers need increased opportunities to develop the ability to filter the many curricular options that are available online.