Tuesday, October 6, 2015

Multiplication Strategies 101

How did you learn to multiply 2-digit by 2-digit numbers?  If you are like me there was only one way and that was the traditional algorithm.  I was never shown another way until I had to teach it to my fifth graders.  I remember reading the following statement: "I can demonstrate, with and without concrete materials, an understanding of multiplication (2-digit by 2-digit) to solve problems.  I remember thinking how am I going to help my students understand this process when I was only taught one way myself.  After a lot of reading, I not only found many great ways to help my students with learning this skill but I found that very few of my students chose the traditional algorithm as their go to multiplication strategy.  Read below to discover some of the ways I now teach 2-digit by 2-digit multiplication and which one became my students absolute favorite!

Array Method

Students make an array using base ten blocks to model the numbers.  They then divide the array into four parts that are easier to calculate.  Finally, they add the four products to get the answer.  My students love trying to figure out my mystery arrays.  You can find these interactive math notebook resources here.

Box Method

Some teachers prefer to call the array method the box method as well.  After modelling many problems using the base ten blocks, I like to move to the box method.  It follows the same method however,  I find it speeds up the process.  Students draw a rectangle and divide it into 4 parts.  They label the box showing tens and ones along the sides.  They then multiply the numbers and add the answers altogether.  I find providing students with small white boards and markers is a great way to teach this strategy.

Partial Products

Some of my students experienced difficulty with this method at first but with the scaffolding provided by using boxes as a guide they soon mastered this method.  The important thing to remember to stress when teaching this method is how to record the numbers.

Lattice Method

This method may look complicated but it is really not that hard once you learn to draw the boxes.  This method has become my students absolute favorite method to multiply.  Even my students' parents loved it once they saw how it was done.  I found watching YouTube videos was the best way for me to master this one.  You can see how it works by clicking here.

Traditional Algorithm

I still teach my students how to multiply using the traditional algorithm as this is the method most of their parents will show them at home or understand from their school days.  I have found that by teaching all the other strategies first it gives my students a much better understanding of this method.  

I have found that by letting my students have the choice as to which multiplication strategy they understand the best and then using it to solve multiplication problems has resulted in increased confidence and accuracy when multiplying.

I hope this helps you to master multiplication strategies of 2-digit by 2-digit multiplication.  Maybe the lattice method will become your new favorite way to multiply!


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