Hi Rebecca,
I love this lesson. I actually completed it for my diploma when I was being inspected about 15 years ago. Although we made volcanoes out a clay first and did not have the reaction in the jar. I love the idea of the jar.
A nice way to introduce the lesson could be a KWL chart and this will maybe keep the children focused and on task.
As a parent myself now, I can see the effect that these inquiry based lessons have on children . My child loves to come home and reenact this type of learning at home. Shame he isn’t as enthusiastic in other areas of the curriculum but it does just prove how important hands on inquiry learning is.