Previous research at the local level on informal observations of classroom teachers by school principals suggests that the frequency of informal observations has little or no effect on teachers' perceptions of school climate. This study employs School and Staffing Survey (SASS) data to examine to the extent to which these results are replicated or not at the national level. We also compare the effect of formal and informal observations on school climate and the extent to which specific teacher characteristics such as being a novice teacher, teaching certain grade levels, and participating in a formal induction program shape the influence of informal observations on teachers' perceptions of school climate. Our findings indicate that the frequency of informal observations at the national level are limited, validating previous findings at the local level. Informal observations do have a larger impact on school climate for novice teachers than formal observations although the difference is still rather small. Two subsections of teachers -- those who teach early high school and those who did not participate in a formal induction program -- tend to have higher perceptions of their school climate when they are informally observed at a greater rate. We conclude our paper by identifying some limitations in the SASS questionnaire and make some suggestions for how questions related to informal observation may be updated for more relevant analysis.