Threshold Concepts (3) Teaching & spacing (…how long is a piece of string?…)

Threshold concepts

I’ve been researching threshold concepts in Chemistry, and have written here about the list of concepts I have collated, based on some research into misconceptions. I am now beginning to teach these concepts to four classes in three year groups (Y10, 11 and 12).

A week or so ago, I set all four classes a pre-topic homework to test their understanding of the key concepts we will cover. In class, I have been explicitly teaching (and referring to) each concept, as it comes up in lessons.

This week, I’ve been covering ionic bonding and structure with year 11. This is an important topic, and the concepts within it form the basis of many key ideas in future modules, so I have been thinking about how best to help them understand and retain these fundamental (threshold) concepts.

Concept 1: ions are always ions (unless they’re no longer ions….)

I am keen to make sure my students understand that once ions form, they become a charged particle that is attracted to any oppositely charged particle, and to appreciate that ions remain as ions, whether they’re in a solid, liquid, or solution. This forms an important conceptual basis for electrolysis and acids/ alkalis/ salts.

So I showed my pupils some precipitation reactions, drawing the relevant ions/equations on the board, and demonstrating how a coloured solid forms when two transparent (sometimes colourless) solutions are mixed. The classes actually gasped!

Screen Shot 2016-11-10 at 23.38.07.pngI talked about how  all the ions are always present in each colourless solution, and once they’re mixed, they’re all still there, but they’ve been attracted to ions “from the other bottle” (and formed a solid).

Concept 2: ions are not “choosy”

I am really keen to make sure my students understand that ions don’t just form bonds with the the ions they exchanged electrons with. I am testing their understanding of this via multiple choice questions.

I used the above questions this week to assess my Y11s’ understanding of some key concepts. They held up A/B/C/D cards to answer the questions, so I could see which questions they were most confident about, and which concepts were still not fully understood. With careful questioning, we had a very useful discussion around the ideas.

Assessing, tracking, spacing (and forgetting)

So I am teaching concepts, giving examples of how they are applied, assessing pupils’ understanding and application, and tracking all this using my concept tracker. This tracking allows me to highlight concepts that pupils had more trouble with (via assessment), so I can come back to them later.


An important part of this process is the retrieval/spacing aspect, and this includes allowing sufficient time for pupils to forget concepts they’ve learned, before reviewing them again later. Damian Benney has written a really thoughtful blog post about research by Cepeda et al. on spacing for optimal retention. He proposes the following relationship between initial teaching and re-study gap.

Screen Shot 2016-11-11 at 16.05.01.png

I’ve taken this into account, and planned in when we will review the concepts encountered in this topic, using the final exam dates for each year group.

Screen Shot 2016-11-13 at 18.47.31.png

Spacing: what are we basing it on?

In putting all this together, I now have a question. The research from Cepeda et al. is based on study participants learning, and then recalling, various facts. But my students are going to need to revisit these concepts before their final exams. They’ll build on them, and apply them to new contexts in future modules, so this is more complext than simply learning and retaining them for a certain date in the summer.

For example, when I teach the “acids” topic in Y11, I’d already noted in my planning that I’ll need to remind students of the concepts above, so that they can apply them to this new situation. However, I do understand that allowing enough time for students to forget concepts is important to retention, so want to take this into account and leave a “forgetting gap” before I review each concept again.


What I’m wondering is: how big is that gap? And what should it be based on? Do I base it on the interval between teaching a concept and the date my students sit their final exam? Or do I base it on the interval between teaching a concept and the time until they’ll use it in another context? And does it matter? I mean- does it make a significant difference?

So, as well as looking at the gap until the final exam, I also calculated the number of days until we do a topic that specifically relies on the concepts that I’m teaching now.

Screen Shot 2016-11-13 at 18.47.40.png

In the end, we’re only ever talking about (at most) a couple of weeks between differing suggested review gaps. And in the context of school life, I actually don’t think that’s a great deal of time.

So I have planned in some checkpoints for in-class assessment and review questions at the end of homework tasks. The concept tracker means that I know which concepts in particular I want to pick up on. I shall see how it goes.

Next steps- confidence grids

I asked some conceptual questions at the start of this topic. I wanted to look at the ideas that students have now, and see how they change as we go through the topic. I plan to ask students to re-visit their answers at the end of the topic and change/ improve them. It also gives me a chance to pick up on any misconceptions, and address them immidiately.

Linda Neeham suggested that I build in some degree of confidence testing to my conceptual questions. I think this will be very easy to do using Google Forms (which I use routinely for homework), and I might look at ways of doing this for in-class quizzes. You can read more about them here, here and here. This is work in progress.


4 thoughts on “Threshold Concepts (3) Teaching & spacing (…how long is a piece of string?…)

  1. This is an absolutely outstanding blog with so much thought and attention to detail. Your students cannot fail to benefit from your application of so many areas of research. I have realised that the graph of mine that you have used above is ambiguous in the meaning of the x axis. The axis is supposed to represent the time from the end of the initial study to the test (not the restudy to the test). This means according to the Cepeda research you may be a few days out in terms of optimal spacing gaps. However:

    “In the end, we’re only ever talking about (at most) a couple of weeks between differing suggested review gaps. And in the context of school life, I actually don’t think that’s a great deal of time”

    I couldn’t agree more with this. And as you point out these concepts are revisited and reinforced as other concepts are covered. It is such an interesting thought about whether concepts and more straightforward knowledge have differing optimal gaps. @pimpmymemory reports that research is being undertaken in this area. And of course all of this is further complicated by the number of times we revisit this information.

    From my work with my Year 10 class I am doing some very rough experiments with the gaps. On some topics I am trialling a pattern similar to: study- 5 days- lag homework – 20 days – spacing lesson and then a gap of 220 days until the exam period. This is based on Cepeda’s data. For other topics I am trying: study- 14 days- lag homework – 28 days – spacing lesson and then a gap of 180 days until the exam period.
    I will be interested to see which gives the best recall after the long RI. However, just to complicate matters, each topic is different with some building more on KS3 prior knowledge and others having more complicated concepts (such as red shift).

    Later in the year when I am going to have just one retrieval event I will exclusively use the Cepeda inspired graph.

    The bottom line is that my students are going to benefit- as are yours. I am going to continue to trial and experiment with different gaps and continue to learn and apply the findings. I will be following your work, and that of classroom practitioners like @MissBKearns with genuine interest.

    Thanks again for blogging all of this. There so much in here to take away.


    Liked by 1 person

    • Thank you so much for taking the time to read this, and leave such an in-depth (and helpful) comment.

      There are so many points to think about further here.
      I guess the main thing is to enable the time to forget before students re-study, if they are going to retain it.
      And, as you say, this time has to be elastic in a school environment, anyway.
      So, for example, I have had to delay the time when my Y11s will re-study until after their controlled assessment period!

      I would really like to hear how it goes with the different gaps.
      Like you say, I think in all this, a key thing is how much it forces you to really examine what you’re doing and why.

      I’m still wrestling a bit with the knowledge vs concepts vs threshold concepts.
      I understand that you need to use key concepts to enable you to understand a threshold concept. But, by definition, I guess once you have undestood a threshold concept, you shouldn’t have to re-visit, because it’s transormational, and your way of looking at things will change?

      I love being able to throw these ideas around and really think about them and discuss them. So thanks so much for the work you’ve done, and the ideas you’ve given me.

      Liked by 1 person

  2. Pingback: Threshold concepts (4) confidence and retrieval | NDHS Blog Spot

  3. Pingback: Hurdles and Bottlenecks (in ionic bonding) | NDHS Blog Spot

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