"You do all sorts of strange things when you're a teacher."

This week I got to introduce my students to multiplication. It was so fun, but I was really nervous! Building the bridge between addition and multiplication is a big step for kids. In my mind, if you do the wrong thing, you could end up with a kid who can spout off facts and solve multiplication problems with an algorithm, yet has no conceptual understanding of what multiplication is.

So how do you introduce multiplication to 2nd graders? My teacher uses curriculum from Everyday Math, so I followed the book, but made my own adjustments as I saw fit. I started with this problem:

Jane bought 3 packs of gum. Each pack has 5 pieces of gum in it. How many pieces of gum did Jane buy? 

Each child had a clipboard with a blank piece of paper on it. I told them to find the answer any way they wanted to. Some of them made 3 sets of 5 tally marks, some of them counted by 5s, some of them wrote 3 x 5 = 15, and some of them wrote 3 + 5 = 8. I facilitated an open strategy sharing in which kids got to describe how they solved the problem. I represented their ideas on the board and then introduced them to the fact that they could solve this problem through multiplication.

What I love about multiplication is that it moves kids from dealing with single objects to dealing with groups of objects. It's kind of like a magic trick. If you need to buy 100 packs of gum, you could either add 5 + 5 + 5 until the cows come home, or you could multiply 5 x 100.

To give them a visual way of representing multiplication, I taught a different lesson on arrays. Arrays are rectangular arrangement of objects in rows and columns. I went back to the problem about Jane's packs of gum, and we made a 3 by 5 array to find the answer another way. After the students did some number stories in their workbooks (number stories = less threatening way of saying word problem), I put a bunch of different objects on the carpet that were arrays. I brought in a cupcake holder, an egg carton, a box of paint, and a chess board. Using these objects, and their imagination, they filled in some blank arrays and came up with their own multiplication problems.

After the lesson, I was talking with my Classroom Mentor about how it went. I told her that I really wanted to bring in an egg carton, but I still had a few eggs in it. I moved the eggs to a padded tupperware container and voila! I had an egg carton. She laughed and said, "You do all sorts of strange things when you're a teacher."

After writing this, I realize that the first strange thing I did was empty my egg container for the sake of a math lesson. The second strange thing I did was gleefully write a blog post about how much fun it is to teach multiplication. Ah well!