Teach your preschool students about colors and rainbows with a couple of boxes of colorful, fruit-flavored breakfast cereal. Add a lesson about sorting as you help your students divide the cereal by color into bowls. Then instruct your students to make a rainbow on a piece of construction paper by gluing the cereal in bands of color. Another idea is to let them string the cereal on yarn for rainbow necklaces and bracelets.
Teach your young students about how primary colors mix to become secondary with rainbow-colored water. Mix red, blue and yellow food coloring into small, clear baby food jars filled with water. Give each student a foam plate and an eyedropper, and let all of them see what happens when they mix drops of red and blue or blue and yellow or red and yellow water together.
Read your students the book "Planting a Rainbow" by Lois Ehlert. Then visit a garden center and bring colorful flowering plants into your classroom. Plant them in clay pots with your students and discuss them in relation to Ehlert's book. Keep the plants in a window and assign a student each day to water and care for your small class garden.
Read your students the book "Rainbow Fish" by Marcus Pfister. After you've read the book, teach them how to make their own rainbow fish out of coffee filters. Give each student a filter and washable felt-tip markers. Have them scribble colors all over the filter. Next, let each student squirt his filter with water until it's all wet. The colors will run, making a rainbow. Once dry, the students can cut out a fish shape and glue on aluminum foil scales. Hole punch the fish and hang them by yarn around your classroom.