I had a week-long "summer engineering camp" for high school students at our college and decided to use this project as the major task for the students. I was concerned because the recommended schedule calls for fourteen 90-minute sessions to complete the project, and we had a number of other activities in order to provide a good overview of different types of engineering. I ended up cutting out the second or "final" test and found that the students could get to the initial test after 8.5 or 9 hours. It helped to have 2 or 3 hour blocks when they could work on building their designs. The one drawback I found was that the constraints did not say that the designs had to be weatherproof. Consequently, 3 of the 4 teams used cardboard to make the frame of the heaters. Clearly that would not last very long in a real world application, so you may want to specify that the designs must be waterproof. The students also got bored during the 45 minute test as it is similar to watching paint dry. It would be good to have another activity for them to work on while they are waiting to take the next temperature measurement. Also be aware that prices have changed since the materials list was put together. I found that lumber products were especially more expensive, so if you really want to stay under the $75 limit, go to the store and research prices before you give out the sheet to the students. Overall this worked very well, and I would definitely do it again.