Now I've never built rocket stoves with my students, but I'm tempted to do so this year in conjunction with our study of energy. The trouble is that most of the students have covered the topic in chemistry (which is not to say that they remember it). It would be a way for us to get some hands-in experience with efficiency and biochar. I'm definitely interested in getting students to make and understand biochar.
These kids are so efficient in their work that this is mainly what I've been doing: