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Algorithms: how to explain them


I like to start by telling learners that this is a genius word!

If you can confidently go home tonight and explain what an algorithm is people will think you’ve become a computer science genius over night!

With that said I then explain that there is a trick to understanding algorithms and that this is to know that they ran actually really simple.

An algorithm is just the fancy name we give a set of instructions when we’re talking about the instructions a computer follows to work properly.

When introducing algorithms to students for the first time (particularly at Primary) two approaches work best and these will be no surprise to any primary teacher I’m sure, they are:

  1. Repetition
  2. Physical movement


Constantly repeating the question ‘what is an algorithm’ throughout the lesson, to different students is my goal here.

By doing this you’re supporting all your learners but also key SEND students who rely on repetition of information even more than the average leaner to solidify new knowledge in their minds.

One tweak to this I’ve learned over time is adapting my expectation for the answer, I may repeat the exact same question throughout the lesson but I expect fuller, richer answers as the lesson progresses and I’ll prompt learners for these answers.

For example at the start I’d accept ‘a set of instructions’ but later I’d expect ‘a set of clear and specific instructions’ and later still id expect an example based activity and later again an example not based on what we did t really show me their understanding and ability to apply what we’ve been learning.

Physical movement

I’ve found that physical activities where possible before accessing technical equipment is a great way to focus on the theory and understanding of computer science and really pays off when you do put a PC in from of a learner.

When teaching about algorithms I like to have learners understand the difference between having instructions, not having them and then having really detailed instructions I having ones which really lack details.

Some example activities which I find work well are:

Sit back to back and explain how to draw an image that one of you has without showing the other or naming the image

Navigate one person around an obstacle course (of desks, chairs and string) by calling out instructions I them – I like to show students a classic tv show Knightmare to demonstrate this before we attempt something ourselves.


The Genius hook!

For me the real hook which I come back to at the end of the lesson is the ‘understand this and you’ll be a computer science genius’. Learners really love to feel they’ve mastered something new and something which is perceived to be really hard to understand. Learners love to achieve genius status!

The gallery here shows some images from an activity I used with my class (in groups) we unrolled a sheet of paper and on it wrote ‘steps’ which made up our algorithm, learners had to follow the steps ans see if they all moved in the same direction and ended at the same point.

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