The children can learn from the products of each other's work, how there is always a choice to be made between depth and coverage. Most children will work on one or two activities in depth, taking several days or weeks to complete those. At other times throughout the project however, these children can also be more superficially involved with a variety of activities, sampling them as it were. For example a child might be particularly interested in tires, perhaps because of an uncle's business, and be making a book about tires. The book may be added to over several weeks.
Dramatic play can evolve over weeks with a few children leading the activity there.
Yet a few children may enter the play only rarely and then at a very simple and superficial level. The teacher can make provision for such differences in level of engagement and enable the children to appreciate which of their friends are particularly interested or expert in which aspects of the study. I'd better finish here for this week. I would like you to be able to help to create a list of examples of activities which you, the teacher, facilitated in response to the learning opportunities afforded by the ongoing project work. These may have involved groups of children or just one child.