This activity will open children’s eyes to something they take completely for granted … bar codes.
I’m including a pdf of my “Cracking Bar Codes” powerpoint slides you can use to show the children, or you could adapt the information yourself and just talk them through it. To be honest, the slides aren’t great – I’m sure someone could come up with a simple worksheet which would take them through step by step, writing down ‘their’ bar code digits as they go.
What you need:
  • items with 13 digit bar codes. (These are the most common, but there are shorter ones which work differently)
  • paper and pen for each child to do the calculations.
  • A4 or A5 sized paper in 3 colours (optional).


Try to include several items where the first two digits are not 50, and several from the same supplier / manufacturer.  You can include books and magazines.  Aim to have one item per child for them to then pass round, so nothing that could be damaged!
I also found it useful to have A4 or A5 paper in 3 different colours to write the bar code digits on for the children to hold.  I allocated 13 children one digit of the code and then sat them on a row of chairs to turn them into a ‘human’  bar code:
Digits 1,3,5,7,9,11  written on yellow paper
Digits 2,4,6,8,10 and 12 on green paper.
The final 13th check digit was written on red paper, so when when they come to add up alternate digits, it is very clear which need adding together and they remember to leave the check digit out of the calculation.  I then called out for yellow or green to stand up so they were added up more easily.
This activity is really only suitable for upper primary.  In addition, more able mathematicians can be set researching how the lines correspond to the numbers (not straightforward) and what kind of ‘errors’ would cause a barcode to be rejected (eg neighbouring digits swapped or a 5 misread as a 6).
The comment about ‘short cuts’ is to get them to think about whether they need to include the complete numbers throughout the calculations or just the units  – in my example do you need to add 30 and 81, or just 0 and 1? This could lead to an interesting discussion and a method of trying to search for situations where this would not be valid.
The check digit (or check sum) concept is used throughout digital communications systems, and most people are completely unaware of it.  However, it is the kind of ‘fascinating fact’ that primary children will love taking home to their parents and then show off that they know how the calculation works.

Activity Idea: Cracking Bar Codes
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