This study analysed 9 to 11 year old children's drawings of tropical rainforests immediately before and after a visit to the Humid Tropics Biome at the Eden Project, Cornwall, UK. A theoretical framework derived from considerations of informal learning and constructivism was used as a basis to develop a methodology to interpret the children's drawings and to measure the change in children's perceptions and learning after their visit. The children's pre-visit drawings mainly showed tree and plant outlines familiar to an English countryside. Rainforest animals were to the fore in the pictures and there was a general lack of scale, depth and perspective in the drawings. In the post-visit drawings, the animals had mainly disappeared. There was often remarkable accuracy in the shape and detail of the tropical rainforest trees and plants now drawn. The post-visit drawings also demonstrated far greater depth, scale and perspective than the pre-visit drawings. The interpretation and analysis of the drawings gave insights into children's understanding and learning about tropical rainforests and demonstrated that analysis of children's drawings can be an effective method of assessing some aspects of their learning. (Contains 2 tables and 4 figures.)