Teacher noticing is a crucial aspect of responsive and ambitious mathematics teaching, allowing educators to understand students' mathematical thinking and make informed decisions. However, this noticing is influenced by teachers' insider knowledge (i.e., past and present knowledge and experience with students), which is shaped by societal norms, biases, and expectations, including potentially harmful deficit discourses. This study investigates teachers' noticing of written work from a situated perspective using qualitative secondary analysis. The goal of this work is to exemplify upper elementary teachers' use of historical knowledge gained from classroom interactions or informal school settings, along with local and broader contextual factors. Data analysis included elementary teachers' noticing mathematical thinking in written work from their class, their use of insider knowledge of their students, and distinctions in orientations toward students and their thinking. Results indicate how insider knowledge enhances, impedes, or does not impact individual teachers' focus on the details and reasoning evidenced in their students' strategies. The findings contribute to a more nuanced understanding of the complexities of teacher noticing and emphasize the importance of acknowledging the socio-cultural and historical context which is needed for equitable mathematics teaching. Implications are discussed.