Time should not bind you.

 A good lesson is "content-driven" as opposed to "resource-driven", and as Adam Boxer (2021) put it, time is a resource like any other. You should plan your lessons based on what it is you need your students to know and to understand, not based on how much time you have. That could be time in terms of "this lesson is 50 minutes" or it could be time in terms of "I have eight lessons before the end of term". Thinking in terms of time will not get you the best version of the desired outcome(s) for your students. Learning doesn't fit into neat, discrete blocks, that coincidentally fit perfectly into the designated curriculum time, regardless of whether you teach in 45-minute chunks, 50-minute chunks, 60-minute chunks, or even 100-minute chunks. Even without getting to the substance of why being time-driven isn't great, you can already see how ridiculous it is to suggest that something, anything, will take "one lesson" to teach.

Adam refers to this idea of being unbound by time as "play[ing] to the content, not the bell" (Boxer, 2021) and argues that this "myopic focus" on discrete lessons removes teacher flexibility The flexibility to adapt to a particularly strong (or indeed particularly weak) class. For me, there are a few more bonuses.

Firstly, and purely psychological, the gaps between lessons, whether that is from one day to another, from one week to the next, or even over a holiday, these gaps don't feel like I'm shutting down. I don't feel like I've stopped everything. There isn't the awkward wind-down to the end of term when you try to wrap everything up on exactly the last lesson without truncating things or longing them out. Instead, when a period ends, you simply pause, and then when the next period starts, you pick up where you left off. No sweat. There's no mad panic as I realise that no matter how fast I cover stuff, I won't be done before the arbitrary deadline. There's equally no mad panic as everyone in the department tries to get the new topic resources printed for the same start date. I imagine in subjects like science, where there is a practical element, this is something the technicians feel acutely. If everyone is expected to be teaching exactly the same lesson at exactly the same time, then when it comes to a practical activity, you're gonna need a year-set of equipment instead of a class-set. I don't know about you, but I'm 90% sure my school doesn't have that kind of funding. [As an aside, I remember being told that "a member of SLT should be able to walk out of one classroom halfway through a sentence and into another and hear the end of the same sentence. Ridiculous].

Playing to the content not the bell means you can really take the time needed to properly develop fluency and understanding. It gives you the freedom to drill down and make sure students have "got it", that they've had a chance to practice it, and gotten useful [probably not written] feedback. Then you can move on. And revisit often. When we develop our understanding of something, when we learn something new, we have to incorporate it into our pre-existing schemata, and that requires a certain about of pre-learning activation of said schema. If the schema is well developed, then activating it will be easier and take less time. A simple question or series of questions will set it ablaze, ready for some new connections to be made. If the schema is poorly developed, then there's a distinct possibility those same questions will be met with a very blank face. Or possibly one that looks straight-up baffled. 

A well-built schema should be easier to activate and build on than one that is less well-formed.

If, when I covered relative formula mass, I was strapped for time, and I skimmed through it, then my students are less likely to have a strong foundation to build on. When it comes to me teaching them about mole calculations, I'm building on sand. The students aren't going to get it properly, it's likely going to take longer than it did originally, in which case if I'm bound by time, I will probably have to move on before they've got it. Again.

I'm very lucky to work in a department where the teaching is content-driven. Because of this, I know that I can think differently about how I'm teaching. It is worthwhile making explicit links to previous content, because I know they will have had the opportunity to get a solid understanding. I know it won't be something that was skimmed over because it came near the end of the topic and the teacher was falling behind and getting itchy. [The flipping pandemic has somewhat put a spanner in the works here, and for most of my KS3 classes I can only reliably do this with content I've taught them. Making explicit KS3 links with my KS4s, and KS4 links with my y13s is still an option]. I honestly feel like my students are getting a much more holistic view of science than my students at say, my previous school where it was very much driven by the bell. They just got a list of stuff that was, to them, presumably related to the previous lesson, but they're not really sure because they didn't quite get it last lesson and now they've moved on.

The downside of "playing to the content" is that is does generally take longer. Science is often very abstract, and so students find it tricky. It can be very easy to get held up by students who just don't get it. But if they don't get it, have we done our job as teachers? Ultimately, it is a gamble. Do you cover 100% of the required content for the course, but to a degree where you're kinda only about 70% confident your students could answer a question put in front of them. Or do you teach 80% of the course really well, so you're 90% confident they could answer any reasonable question? Personally, I'd go for the latter. I'd probably also hedge my bets by giving the students a bunch of videos to watch on the remaining content. Just in case.

TL;DR

"play to the content, not the bell"

Boxer, A., 2021. Teaching Secondary Science: A Complete Guide. Melton, Suffolk, UNITED KINGDOM: John Catt Educational, Limited, p.35.

Raichura, P., 2020. Building understanding. In: The Chartered College of Teaching, ed., The Early Career Framework Handbook. London: Corwin SAGE, pp.55-67.