General matra for teaching: this year’s students would think that previous year’s students weren’t challenged.
This is hard to measure in the short term and hard to implement. In some cases you hit a particular topic and it’s easy to find more depth. In other cases what you’ve been using for a couple years is probably exactly what you want. What’s interesting is that I seem to be finding less and less to modify in a lot of situations. Or maybe I’m not trying as hard as I used to? Teaching Calculus has been the greatest challenge of my career and there seems to always be something more you can be doing.
Below is a classic example. In 2012 I had Pre-Cal students make some simple sketchings of pre-made sin/cos functions. By 2016 they were creating their own from a list of requirements and writing paragraph long descriptions. That’s the goal. A 2016 student would be blown away at how simple things used to be. But can you keep that up so 2020 says the same thing about 2016?
It’s a problem I think about all the time, especially now. I have been purposefully making myself work less, trusting what I did in the past and making only minor tweaks. But it always seems there are ways to improve what you did before, you know?