I suppose I should already know this answer, but I have never used this feature before. If you choose to “close” a response, does that mean the students can no longer participate in the Formative or what exactly does that mean?
Yes exactly. However, they can still access the whole Formative.
Closing just means that they can’t enter responses, but they can still view the entire Formative. If you want to hide it from their view, you have to unassign it.