Pick a warm, dry day for this lesson. Have the tables already set up with the soil samples and measuring tapes. Tell the children to put on their smocks and find a place at the tables.
Explain that they are going to learn about soil texture. Tell them to take a small pinch of soil from cup #1 and roll it between their fingers. Ask the children to tell you how the soil feels. Tell them what they are feeling is the soil's texture. Soil is made up of many tiny pieces of broken rocks, minerals and sand mixed with decaying plants and creatures.
Instruct the children to take a pinch of the soil in cup #2, and roll it between their fingers. Ask them to tell you how this soil feels different from the first soil. Encourage them to use the word "texture" in their answer. Ask them to compare the size of the particles in the two samples. Repeat the process with soil in cup #3. Ask them which soil they think allows the most oxygen and water to reach plant roots.
Wet the soil in cup #1 using just enough to dampen it without making mud. Show the children how to roll it in their hands to form a ball. Tell the children to repeat what you have shown them with the soil in cup #1.
Squeeze your hand slowly, making a ribbon of the soil come out between your thumb and index finger. Tell the children to repeat what you have shown them. Ask them measure the length of their ribbon. Have them identify the type of soil using the following information. Sand will not make a ribbon and is difficult to roll into a ball. Its texture is gritty and grains of sand will stick to their hands. Loam will make a ribbon of approximately 2.5 cm. The ball has a spongy texture, and will not feel gritty. Clay will make a ribbon of 5 cm, or longer, and have a smooth texture. Repeat with the other two soils.
Ask the children if they have changed their opinion about which soil texture allows the most oxygen and water to reach plant roots. Explain that loam is very good for most gardens because oxygen and water can move easily through it. Sand has large particles and pores that allow water to move through it, but it dries out quickly. Clay is made of tiny particles with few pores. It can also get hard, but once it is wet, it holds the moisture longer.