Yesterday I was zapped. It had been an unexpectedly busy weekend, and a very rainy, muggy Monday. I wasn't alone as the students and several colleagues looked like they were experiencing a similar kind of day. As a new teacher, a day like that would worry me as I simply didn't have the energy or zest for the more challenging teaching tasks. Instead of pushing myself through it, I chose to teach a number of activities that were less energy intensive and move through the day peacefully. That was the right thing to do as today I'm back filled with my usual quotient of energy and enthusiasm.
Teaching is intensive work. There's lots of one-to-one and one-to-many time on task activity. There are also lots of emotions. For example if a child comes to school sad or upset, that weighs on a teacher's heart and mind too. Further some teaching tasks are simply more intense than others. That's why I like to think of good teaching as harmonious choreography. You choreograph the day to match your mood, the students' disposition, the weather, the schedule, and multiple other factors. If you keep all the lessons and experiences you've planned to lead right by your side, you can pick and choose the best fit for each day and each section of the day. That lends itself to a positive routine and happy, successful students too.
So rather than fight the low days, simply give in to them and teach the lighter, simpler lessons, and save those intense, energetic lessons for the days when your energy is high and enthusiasm full. Onward.