Whilst at a sandpit or beach location, encourage the child to dig a hole as deep as they possibly can. They can use their hands or a small spade. Before they get started, ask them to estimate how deep they think they can get (widening the gap between both hands to demonstrate).

As they dig, ask them whether they notice any changes in the sand as they dig deeper. For example, Does it feel wet or dry? Crumbly or sticky? What else do they notice?

If the sand is falling back into the hole, explain that this is happening because the sand is dry, so the small particles aren’t sticking together. Whereas, if the sand is forming clumps, it is likely to be moist or wet. Add that the deeper they dig, the wetter the sand could be.

Introduce the concept of width and depth using the freshly dug hole. Explain that we use words like ‘deep’ or ‘shallow’ to describe the depth of the hole. Next, point out the width. Use a ruler, measuring tape or your hands to measure the width and depth of the hole and say the results aloud. E.g. The hole is 30 centimetres deep and 10 centimetres wide, or 2 hands deep, 1 hand wide.

Next, ask the child if they think they can dig a hole horizontally (a tunnel). Encourage them to consider some of the challenges. E.g. It’s much harder to use a shovel and it could cave in due to the sand on top.

Encourage the child to dig a tunnel in the sand. Before they begin, ask if there is anything they might be able to do to keep it from crumbling. Invite them to have several attempts, talking through what they are thinking and the challenges they face along the way.

Demonstrate some ways they could increase their chance of the tunnel staying up. Including:

Adding reinforcement – Use small sticks or bark to support the roof of the tunnel. Show how placing these supports at regular points can help prevent the tunnel from collapsing.

Adding pressure – Compacting the sand (pressing it down) gently can make the walls and roof more stable.

Adding water – Adding a small amount of water can help the sand particles stick together, making the structure more solid. Demonstrate the right amount of water to use to avoid making the sand too wet and heavy.

Once the child has succeeded at constructing a tunnel, measure it and compare the results to the vertical hole. Ask them to comment on which was most challenging and the reasons why.

Before packing up, help the child make connections to real tunnels they may have seen (i.e. walkways, roads, or railways). Explain that these tunnels are designed by engineers and involve lots of problem solving and maths.