I've only gotten that question as a sub, and thankfully then I can very honestly say, "I have no idea." My 2nd and 3rd graders though ask (on Fridays) "Do we have school tomorrow?" and my reply is always, "YOU do!" It's probably mean but it's hilarious. The kids who were in my class last year know I'm just messing with them and say, "Miss M!" The kids who weren't in my class have a momentary expression of confused panic that makes it totally worth it. Same goes for when they get a huge packet from their teacher and start freaking out about having to do all of it (even though it's classwork and they're clearly going through it together), and they ask if it's homework: "Yup, you have to do all of it tonight. It's due tomorrow." I'm a mean teacher.... But it's just so funny to freak them out when they ask questions with obvious answers if they would just THINK about it for 3 seconds before asking.