Be ready to call an audible.
This was advice I got during my third year teaching. I had just transferred from Seward Park to Stuy and was being observed for the first time by my former teacher and now supervisor Richie Rothenberg. I forget exactly what the lesson was on - something with coordinate geometry I think. The lesson was okay but it wasn't going over well with the class. I was teaching at too low a level for my audience. I could feel it as I was teaching but as I was pretty inexperienced I wasn't confident in changing things up on the fly.
Afterwards, Richie and I debriefed. He said the lesson was satisfactory - the magic word you need on any observation but that it could have been much better. I had only been teaching at Stuy for a few weeks and even though I was a Stuy grad I hadn't had time to get my head around where the students were at. Richie said that sometimes you just have to call an audible. For a young teacher, easier said than done. In addition to not having a great handle on my students yet I also wasn't confident in flying without a net.
This is why it's so important for teachers to really know their stuff - both the content and how to teach it. It's why I'm concerned when I see so many leaders in CS education pushing scripted curricula and PD based training to fully "prepare" CS teachers in just a few PD sessions.
First time through, particularly when you're voluntold to teach a new class you just want to survive. Follow that script, learn with your kids and get through. You'll grow and the kids will be richer than had you not gone through the fire with them.
Two or three years down the road, however, if you're still just following the script you're doing your students a disservice.
Of course, having subject knowledge doesn't mean you have all the answers but it lets you call that audible when a class needs something that is not in the lesson plan or lets you talk about multiple positions on subjects with no single best answer like coding style.
And then calling an audible isn't always about making a lesson more advanced. It can also be about sensing what a class needs at that time. This is something I learned from Bruce Baskind at Seward Park. I've lost touch with Bruce but he was a mentor and a friend when I started this teaching thing and without the support I got from Bruce and a handful of others back at Seward, I wouldn't have made it.
Sometimes, you've got to turn off the academics. A class might need a team building exercise or maybe just something fun. They might just need to turn off school for part or all of the period. Sure, you burn a lesson but sometimes that's what the kids need and at the end of the semester, they'll be further along for it. I'd sometimes take a block of class time and do Story Time - literally right out of grade school - usually something from The Stinky Cheese Man like "The Really Ugly Duckling." In some ways it's related to the Halloween Stuff I used to do at Stuy. Those were preplanned but that was all about relationship building with the class - the non academic stuff that supports the academics the rest of the year.
As this post is beginning to wander I think I'll stop.
Next up - a specific audible I called that, at least for one student, turned into a very memorable lesson.