Give each child two or three beans and a Styrofoam cup. Allow them to scoop their own potting soil with a small spade and place their beans about one inch under the dirt. Explain the growing process to the class. Ask them to name the things that plants must have to grow(sunlight, water, soil). After each child has planted their seeds, put the cups on a cookie sheet or on a cardboard box top and line with paper towels.
Keep the plants in the classroom for two weeks. Observe the plants each day, making notes on large chart paper about growth progress. Allow the children to take turns watering plants and placing them in different positions in the room so they can see how direct and indirect sunlight affects growth. Taking pictures with a digital or cell phone camera every two or three days is another effective way for preschoolers to view changes in their seeds.
Allow the children to take their plants home. Send a letter to parents encouraging them to help their child maintain and transplant the seeds to a bigger container as they grow. As an incentive, you can have a contest in which a prize is awarded to the students who bring back the tallest or most well-cared for plant. You can have another teacher or the preschool director be the judge.