A system is a whole that is composed of parts arranged in an orderly manner according to some scheme or plan. In science, systems involve matter, energy, and information that move through defined pathways. The amount of matter, energy, and information, and the rate at which they are transferred through the pathways, varies over time. Children begin to understand systems by tracking changes among the individual parts. Older children might gain an understanding of systems by studying the plumbing or heating systems in their homes.
Scale refers to quantity, both relative and absolute.
Thermometers, rulers, and weighing devices help children see that objects and energy vary in quantity. It's hard for children to understand that certain phenomena can exist only within fixed limits of size. Yet primary grade children can begin to understand scale if they are asked, for instance, to imagine a mouse the size of an elephant. Intermediate grade children can be asked to describe the magnification of a microscope. We can create or design objects that represent other things.