Mrs. Berman and I are trying to encourage our kiddos to meta-cognate so a frequently asked question in our room is "How do you know?" While counting the days of the month, we'll ask "How do you know 19 is next?" Kids playing at the water table who are talking about the temperature of the water are asked "How do you know it is going to be cold water and not hot water?"
Metacognition is thinking about your thinking and learning about how you learn. It is a very valuable skill that all of to practice. And it's pretty fun to see the looks on their faces as they try to figure out exactly how do they know that ice in the water is really going to be freezing.
