I suscribe to the NRich newsletter. This site provides tons of math puzzlers and problem solving strategies for all levels of mathematics. This week's newsletter included an advent calendar. Behind every little train "door" is a different activity to do with your class. This morning I started with Day 1. I know, a little late, but at least I'll get six more days in before the break! Day 1 is enough on it's own to get you hooked. The kids absolutely had a blast trying to figure it out. And I had a blast with them! The site provides print outs for the activity and teacher instructions along with extensions. I can't wait to do Day 2 tomorrow! Check it out! Click on the picture of the advent train to be directed to the activty.