Teacher: How to visually format questions/answers to easily follow the story?
Student: I think that using "T" as prefix for Teacher and "S" as prefix for Student may help. You may also use the full word (see also) at the beginning. Do not omit this if roles can be inverted or the flow will be soon unclear (unless this is your creative intent.) Consider to repeat the full word when normal T/S/T/S sequence is subverted (like in this discussion.)
T: You're right but how can you distinguish between questions and answers?
S: I think you don't need to, after all questions are short and they probably end with a question mark, a visually uninterrupted flow may be read as a fluent speech instead of a bulleted list of points.
T: I'm not sure it's enough and not all questions end with a quotation mark. Also note that question text might become pretty long and it may be easily confused with other answers. Take this one, for example.
S: I think it may be useful only to quickly browse the questions to find a specific point but, if you really think it's not enough, you may use some subtle formatting like italic to denote questions. Alternatively another (paired) font, clearly distinguishable from the normal one (in size and/or style). I am a mature guy but if the book is for young children then you may use a serious font for the teacher and a comic one for students. In the Chicago Manual of Style QA, for example, questions are dimmed and printed in gray. I don't especially like it: you put emphasis on answers but often questions are as much important as their answers. APA suggests to use bold for questions but it may be visually distracting and it puts too much emphasis on questions.
Student: What do you think about it?
T: I admit it may work, if questions are not too long then even just italic won't add too much noise. In this way I may also keep color for something else (if any). If I'm not wrong I think I saw this technique (sometimes using bold or even bold italic) used very often in printed magazines. I think I saw also answers in italic and questions in bold but that makes everything confusing: I do not want to read a long text in italic and I do not want to over-empathize questions unless they're searchable titles.
Teacher: Do you have any other idea instead of italic/bold text, just in case? I'm not sure they fit graphical style I have in mind.
S: An answer is logically related to its question then you may also drop italic text and use indentation. You may also use them both, in typography the limit is only our creativity.
T: Can you give me an example?
S: Of course, it's my pleasure!
T: Do you think it works?
S: Yes! Clear spatial separation may also help children to follow the path.
Note that above suggestion applies to traditional printed material, electronic and/or interactive content has more options and you do not have to keep it simple because of printing costs (color Vs b&w and text Vs imagery/graphics). I'd suggest to also ask to your typographer, their experience is invaluable.