In first grade I have the children paint drawings of balloons using the primary colors, then the secondary colors (which they mix right on the paper), then tints, then shades. This year we're doing the Middle Ages so I had them do this, only on a stained glass window that they drew and outlined in black oil pastel.
In grade two they make paper collage robots. First they write their color scheme on an index card and list the colors they'll be using. I keep a chart of the following color schemes in the art room where all can see it: primary, secondary, monochromatic, complementary, analogous, warm and cool.
Third graders use these color schemes to weave paper mats.
Fourth graders use them to weave with yarn. They make mats, pillow, purses or wall hangings.
Fifth graders use them for printmaking or mask painting depending on what goes best with the theme for the year .
The idea is that by fifth grade they are thoroughly familiar with color mixing and color schemes.