The playroom dollhouse fitted with model solar panels and a rain barrel gives one clue about the Circle of Life Cooperative Preschool's approach to conservation. The recycling bins and compost piles only confirm the Frederick preschool is the sort of place where a banana peel doesn't go to waste. The school's efforts were acknowledged on Friday, when it earned a title as one of America's greenest classrooms. Parents entered Circle of Life in a competition sponsored by Malt-O-Meal cereal and TerraCycle. They were surprised to learn the small school was one of the top 10 vote-getters on Facebook. Based on "green criteria," a panel of judges chose three first-place winners and a grand prize winner from the final 10 contenders.