Click here to see other posts in this series:
The background context
Part 1 (this page)
Part 2 of how I sequence my lessons (lesson types in the sequence)
Part 3 of how I sequence my lessons (Guided application and linking knowledge)
Part 4 of how I sequence my lessons (Application of knowledge)

How I sequence my lessons in science thinking about time and interleaving

I think all science teachers have same end goal for their students (whether they are self-proclaimed progressive or traditional in their style): flexible knowledge. What's the difference?

Inflexible knowledge can only be used within the context that it was learnt
Flexible knowledge can be applied to new and different contexts

Let's take an example. Here are some application-of-knowledge questions I have written for the topic of particle theory taught in Year 7 (11-12 year olds). The little number next to the question is the number of marks available:

However, inflexible knowledge must come first. Students are introduced to new material in carefully planned ways, but then our job as teachers is to move the students forward towards flexible knowledge. So how do we get from inflexible to flexible knowledge? This series of posts intends to show how I attempt to get there through the questions I use and the sequence of lessons I employ.

Considering cognitive load theory

All teaching should be informed by Sweller's cognitive load theory.
A good poster on the basics of cognitive load theory here
Flexible knowledge is hard achieved and any application of knowledge in one lesson is probably a good show of performance rather than learning. The problem we have in working memory which are the items and processes we can process at any one time. This isn't many and if we are asking students to remember content they have only just been exposed to, and also to have spare working memory capacity to apply this knowledge to a new context, we are asking for failure. It is simply too much. Application of knowledge to new contexts requires all the spare working memory capacity we can get.

I teach mixed ability classes with, sometimes, a vast difference in working memory capacity amongst the faster and slower students. If I really wanted my students, including the slower ones, to have spare working memory capacity to be able to apply knowledge, then I must reduce the cognitive load:

Reducing intrinsic load (the difficulty of the task)

We can free up working memory capacity by having students transfer some of that load to the long-term memory. I want as much spare working-memory capacity as possible for my students to used it on applying their knowledge, not trying to remember what the correct knowledge is. In other words, I need students to memorize core knowledge in science so that it is available for use at any time without putting extra load on the working memory. But this takes time, and when I first implemented retrieval practice at the beginning of every lesson, I was astounded by how much practice was needed before my weaker students began to remember core knowledge.

Now, every lesson begins with retrieval practice.

Every lesson I plan that includes implicit teaching of new content has its associated “core questions” (with hat tip to Adam Boxer @adamboxer1 for his influence, he speaks about core questions here). These serve three purposes:

It helps my planning as I have to define the exact details that I want to be learnt in my curriculum
They help me to focus the students' attention on exactly what they need to remember when I summarise what I have taught in that session (amongst any informational noise from side discussions/questions that may occur)
It allows them to focus their practice on that core knowledge at another time (in lesson, at home, in a substitution lesson).

Consider the example below. This is one set of core questions, and so is linked to one lesson in which I implicitly teach a new concept, in this case, this is the first core question set from the topic of particle theory in Year 7 (11-12 years old):

These core questions form the basis of retrieval practice in my class, but I have some other question types that we will get to in part 3.
Students enter the classroom as a routine and carry out zero-stakes (I don't take in marks) “core questions” from a topic of my choice. Many times we will do two sets, the first set being from a different topic that needs revisiting, but then a another set from the current topic. Newer memories tend to be weaker (they've had less time to be practiced), and I want my students to be able to access the lesson fully, therefore a quick set of core questions from the previous lesson on this topic can be useful

The students enjoy it; for many it is like a pub quiz, they enjoy “knowing things” and just as I learnt from psychology studies: success leads to motivation. The answers are shown immediately for feedback and students mark their own answers. Using our online platform on Frog, students have access to all the types of questions I produce from home and I encourage practice. Here’s an example of my “core questions” format,

To read why I prefer to have the questions in tables, go here

Learning takes place over time and requires practice

Students will not learn much on first or second exposure. All humans forget things, and we can forget things quite quickly. Ebbinghause's famous forgetting curve shows us this clearly:

To give students time for practice, I don’t block my topics; I interleave them. This means I don't teach a topic lesson by lesson, but I am often in the middle of three different topics at any one time. Look at the picture below, the colours show the topics and each lesson is a square. I have raised the blue lessons to show how one topic might be spread:

Spaced learning is proven to aid in learning, by giving students enough time for those memories to weaken (maybe even close to forgetting) before retrieving them, it will make those memories stronger. But I also see an additional benefit here, and that is that I need to give my students practice time within a topic before I move to the next lesson.

Science content is always cumulative, and it is likely that the knowledge from one lesson is required to fully access the very next lesson.

By interleaving my topics I have a longer time frame before the next sequential lesson of the topic, which gives more opportunities for retrieval practice with core questions. The slower students get the time required to form long-term memories and the faster students get to benefit from "overlearning".