In looking forward at my plans to become a mathematics teacher, the importance of questions in class seems almost painfully obvious. At some point, every student has had teachers on either end of the good-questioning spectrum: teachers who have lectured without asking questions of their students or allowing their students to ask questions of them, and teachers whose instructional style is built around questioning and exploring what captures students' curiosities. When I'm a teacher, I'd love to be the latter.
Questioning is a powerful tool that allows students to have agency in the direction of their own learning, in ways that simply lecturing or giving students pre-determined work can never do. The open-endedness of questions students receive from the teacher allows for students to explore their own thoughts and possibilities individually, and the questions students ask the teacher allows the teacher to understand their students' thought processes and hang-ups.
Consider text-based games, like the one pictured below. What would be the fun in a game like this if it weren't oriented around questions and open-ended directions? If the game told you each step to take individually, it would lose all its excitement and there'd hardly be a point in playing it. The same goes for education: the most valuable experiences come from guidance, not explicit instruction.
I was always impacted by good questions when I was a young student, and in math classes especially there were two questions, or types of questions, that stood out to me as particularly helpful for my development. The first, and one of my favorites, is "could you explain this to the class?" or, better yet, "could you convince your classmates of your answer?" This question is valuable because it forces students to reason beyond just the act of finding an answer, gives them agency in describing why their answer makes sense to them, and allows them to talk to their classmates to explain problems and concepts in ways that might not be immediately clear to me as the teacher. When selecting and sequencing within the five practices, these types of questions can allow particular students to guide the whole class in a certain direction that the teacher anticipates in advance, without making it seem like that guidance is explicit. They make student presentations more valuable and more helpful to the class as a whole.
Another question I often come back to in math education is a simple but powerful one: "what else?" Students often fixate on getting the "one correct answer" in math, and have trouble seeing the flexibility of math and understanding the notion that sometimes mathematical concepts have multiple applications and answers. If I as the teacher am aware of something additional that I want students to know with regard to a mathematical topic, finishing up an explanation or solving a problem and then asking "what else?" allows the students to think on their own about what more I might want them to consider. Again, the importance of questions to me is all about open-endedness and letting students explore possibilities themselves, instead of having me do all the guiding and having the students passively listen.
To close out, I want to point out that even in non-classroom contexts questions are the keys to learning. Take a look at one of my favorite Bill Nye episodes below, and count the number of times Bill asks a question. There's no classroom or audience to answer, so why does he ask so many questions? Hmm...