A pile of sand, a sandbox or a sensory table full of sand are tools for imaginative play, sensory exploration and science investigations.  In the April 2013 issue of Science and Children, the Early Years column, I wrote about how children wondered what made a series of cone-shaped pits in a line in the sandbox. Their question came after a long period of unstructured play and it inspired an investigation into how water can move sand.
As children work with dry and wet sand, they notice and make use of the differences due to the properties of water:

• Wet sand sticks together and can be made into deep holes and tall “mountains.” Footprints and other impressions are easy to make and see in wet sand.
• Dry sand can slide off a shovel and flow into a hole or fill a bucket.

The water molecules adhering to sand grains and each other aren’t visible to the children but they can explore this property, and think about how that is the same or different from the way other materials behave.
Some teachers bury small objects, such as shells, for children to discover while digging. In nature, sand and other sediments cover and bury objects and previously laid down layers of sediment.
Using a magnifier children can see the shape of the sand grains and notice different colors.
Children may notice the temperature differences between sand in direct sunlight and sand in the shade.
Impressions made by feet or objects can be filled with wet plaster of Paris (mixed by an adult in a plastic bag) and later pulled out of the sand to reveal the cast of the shape. Some fossils are formed when the space that a dead plant or animal occupied is filled with minerals over time.
Early childhood programs that have a water source that can be used with the sandbox provide an opportunity for children to create and observe water flow. As children work, ask them to tell you what they notice is happening. Record their words, have them write or draw about their observations. This documentation, along with their recollection of the experiences, is their evidence for any statements they make about the properties of sand and the force of moving water. Talking about what they observe is an important part of learning. Sharing their ideas about why and how is part of “doing science.”
These early childhood investigations and experiences support later learning about properties of liquids, engineering design, earth science concepts such as erosion and sedimentation, energy, forces and motion, and systems. Take a look at the Next Generation Science Standards (NGSS) for K-grade 2 and see how the performance expectations (and the practices, core ideas and crosscutting concepts they were developed from) are supported by sandbox play and investigations. The NSTA has guides to the NGSS to help us use them in teaching children from early childhood and up.