The child's knowledge of nature's relationships will develop over many years. Ideas will be visited again and again in new contexts and with greater detail. Such concepts as energy transfer, gravitation, photosynthesis, and the water cycle will build slowly as children mature and learn in different contexts. In the early years the curriculum should focus on experiences and ideas that are accessible to children - for example, how planets differ from the earth or the variety of materials found in nature. The curriculum should build on the first steps to understanding, using what children can observe - the movement of the sun and moon, the patterns of seasonal change and changes in the earth's crust that are evident to anyone who looks for them.
Young children are especially curious about how the world works.
In the early grades, young students can start with the ways organisms, themselves included, modify their surroundings. For example, as people have used the earth's resources, they have altered some earth systems. By the end of 2nd grade, students should realize that some events in nature have repeating patterns. They should be aware that chunks of rocks come in many sizes and shapes from boulders to grains of sand and even smaller. Students should learn what causes earthquakes, volcanos and floods and how these forces shape the earth's surface.