Research Findings: The aim of this study was to investigate U.S. preschool teachers' math pedagogical content knowledge in number comparison. Seventy-four in- and pre-service teachers completed a set of scenario-based questions from a researcher-designed questionnaire that is composed of learning scenarios. Through a mixed-method approach, the study revealed the following findings: a considerable portion of participants (89%) successfully identified the concept of number comparison embedded in a learning scenario, showcasing their specialized content knowledge. However, when it came to knowledge of content and students, only 24 participants (32%) were able to pinpoint both a child's mathematical strength and area of need. In terms of knowledge of content and teaching, more than half of the participants (51%) recommended the utilization of hands-on materials and/or visual aids as part of their remediation techniques, while 49% did not reference these educational tools. Notably, no significant differences were observed between the pedagogical content knowledge of pre-and in-service teachers concerning number comparison. Practice or Policy: The findings indicate that teacher education and professional development should focus on helping teachers understand children's learning trajectories on number comparison and include instructions on using concept specific developmentally appropriate strategies, and indicate that teaching experience cannot replace professional training.