In October 2020, the Canadian Teachers' Federation (CTF/FCE) released the "Canadian Teachers Responding to Coronavirus (COVID-19) -- Pandemic Research Study. National Summary Report. Overview" (ED610460). That document is an important baseline for understanding the impacts of teaching during a pandemic, and supports needed for teacher mental health as the COVID-19 pandemic unfolds. This "CTF/FCE Mental Health Check-in Report" analyzes the follow-up "pulse" style CTF/FCE Survey on the mental health and well-being of teachers in the 2020-2021 school year, documenting the continued detrimental effects of the prolonged pandemic on teachers' mental health and well-being. The (CTF/FCE) Mental Health Check-in Survey was conducted in both Canadian official languages from October 16-25, 2020, with a total of 13,770 completed responses. The CTF/FCE Survey was voluntary, and applied to educators who were currently teaching in the 2020-2021 school year. Response frequency for the Survey was very high, averaging almost 570 responses per day over a ten-day period (568 responses/day). Comparatively, the Pandemic Research Study in June, 2020 garnered an average of 216 responses per day and a total of 15,119 responses over a two-week period. This shows the current Mental Health Check-in garnered almost double the frequency of responses even over a shorter Survey timeframe, signaling the importance of mental health as a topic. The Survey was distributed through CTF/FCE Member Organization networks and through snow-ball recruitment using social media platforms, Twitter and Facebook. The CTF/FCE Mental Health Check-in Survey comprised of ten closed-ended questions on mental health and well-being, and included baseline questions on teachers' current mental state and stress levels, Likert scales on emotional and physical well-being, and comparative longitudinal questions. These questions, replicated from the June 2020 CTF/FCE Phase One study, offer longitudinal data on teachers' baseline feelings of well-being, the state of their physical health, and their top concerns for their mental health and well-being. A comparative discussion of these longitudinal results appears in this report. This report provides a detailed analysis of the ten close-ended questions on mental health and wellbeing from the CTF/FCE Mental Health Check-in Survey. Results from demographic questions appear in the Appendices of this report. Analyses are displayed in graphs, heat maps, and frequency charts depending on the question. Each question is then broken down and discussed using key results, and comparative longitudinal markers from the June 2020 Survey.