Within the current era of educational reform, greater numbers of early childhood teachers have become engaged in teaching mathematics curricula that require teachers to have a deep understanding of children's mathematical thinking. The purpose of this study is to examine how pre-kindergarten teachers in the United States (US) notice and interpret children's mathematical thinking. To address teacher knowledge of children's mathematical thinking, a qualitative case study was conducted. The sources of data include classroom observation and post-observation interviews with each teacher. The results indicate that these teachers varied in their level of noticing and attending to students' mathematical thinking. Although some teachers could successfully engage their students' mathematical thinking, the extent to which they interpreted that thinking was different. (author abstract)