Science
Science in High Scope works exactly like Math in High Scope, except for the Key Experiences for Science being different from those for math.
Volume
The sand and water play is excellent for teaching the concepts of volume, mass, density, and a good few others.
For example, by filling and emptying containers of different sizes the children not only learn the practical skills of handling the materials, lifting, pouring, mixing, etc. but they also learn that the sand that fills the small cup doesn't fill the large one and that the water in the big container won't fit in the small one.
Density
Some things float on water, others don't. It is not necessarily the weight that makes them sink since some heavier objects do float and some lighter ones sink so children learn the concept of density in a practical way. Some things made from the same material float because of their shape.
There is no limit to what children can learn from sand and water play and it is very important in High Scope. This is why I have a sand and water play area inside the house in addition to the ones outside.