Intentional Interleaving in Economics Delivery & Practice

Intentional Interleaving

This post provides economics examples (from teaching UK A Level Edexcel Economics A specification) related to my 'The Shape of It' mathematics example given in my previous blog post, 'Turn over a new leaf...'. Please read that post for wider discussion and general understanding of interleaving.

Teaching Elasticity

Students of A Level economics need to understand and be able to use four types of elasticity – price elasticity of demand (PED), price elasticity of supply (PES), income elasticity of demand (YED) and cross elasticity of demand (XED). These concepts are all similar in many respects, but each is slightly different.

Previously I have taught the definition, formula, calculation, interpretation, diagrams and factors affecting PED and then provided students with practice on this sub-topic. I have then proceeded to teach PES and provided practice. This would be classed as ‘massed and blocked practice’. After PES (I am bored of the repetition by this point) I’d hack my way through XED and YED and offer some practice on those too. I’d do some practice on all four mixed up together (this would be interleaved practice), but relatively little as by this stage I’d need to move on to teaching the next few topics otherwise we’d never finish the unit! I often didn’t have a great amount of time to come back to this later on either.

Reading about interleaving (and spacing) highlighted the rather obvious (hindsight is a wonderful thing!) idea that I would probably be better to cut some of the initial blocked and massed practice in favour of more interleaved practice at the elasticity topic end point and also later on. So I have changed my approach and deliver relatively little post-sub-topic immediate practice, more interleaved practice after teaching all four sub-topics and more spaced interleaved practice by covering this again multiple times later on in the unit and the year.

The purpose of this exercise is to improve student abilities in discrimination. All PED calculations are done in essentially the same kind of way and the answers to these calculation questions are nearly always negative answers. PES, XED and YED calculations each vary slightly and answers can either nearly always be positive (PES) or be either positive or negative (XED, YED). Blocked, massed practice fails to expose students to the reality that in the exam they will be faced with an elasticity question and they must select the correct method and interpret the answer appropriately. Blocked, massed practice typically fails to guard students from the surprisingly common mistake of missing out the positive/negative sign in a PED/PES answer (they remember every time when they do their PED-only and PES-only massed practice though!) and it fails to test with rigour the fact that positive YED answers indicate the good is ‘normal’ whereas positive XED answers indicate the goods involved are ‘substitutes’ (students nearly always get the positive-normal idea right in a full set of YED questions though and the positive-substitute idea right on a full set of XED questions). Interleaved practice however gives students the opportunity to practice choosing the right approach and correct interpretation key and answer format.     

Government Intervention

I am adopting a similar approach to teaching and practice of methods of government intervention. There are 8 interventions that students must cover at AS level. Delivery of each followed by immediate practice of each (e.g. tax content, tax case study, subsidy content, subsidy debate etc.) would appear to be less effective than teaching all 8 interventions and then offering mixed practice on all 8 after this and again at spaced later points.