Great piece. I also thing it is not a great idea to have students follow along with the demo. Just ask them to watch and ask questions first and then leave as much (if not more time) for them to go through the tutorial at their own pace. For example, when teaching Git I spend some time drawing out the workflow, then model a successful commit, and then ask everybody to follow suit at their own pace. At this time I would normally walk around and help any stragglers.