This paper presents part of an evaluation of a new children’s programming environment, developed by Apple Computer Inc. for 10–13 year old children. We studied 56 children, generally working in groups of 2–3, using KidSimTM for between 2–12 hours, over a period of between 2 days and 3 weeks. The results show that children of this age can readily learn to master the programming environment, and that they greatly enjoy using the system — indeed in most cases it clearly fired their imaginations. However, questions remain about the level of programming abstractions that they were able to understand.