Whether this estimate is close we'll never know, but it does call into question our ability to approximate.
To do this you could set up a "guesstimation hub" in a corner of your classroom. Label a jar the guesstimation jar and fill it with dried peas, for example. Now let pairs of children visit the jar in the hub and guess how many are inside. They can write down their guesstimate on an entry form and deposit it in a box labelled the guess box.
At the end of the day you can reveal how many are inside and compare these to the range of guesses. Share strategies and thinking used to make the estimations and record these on a chart.
The closest guesstimators get to fill the container with something of their own choice. For example, they might choose matchsticks, pencils, sweets, dried pasta, coins, stones, and so on.
Try this with containers of different sizes and shapes and watch pupils'
approximations grow in accuracy.
John Dabell is a numeracy consultant and teacher trainer.