Monday, October 8, 2012

Multiplication Mania

Hello all,

I thought the blog format would be a great place to share a math teaching ah-hah moment I had on the Friday before Thanksgiving.  Usually a day that the students are a little checked out on with the three day weekend approaching.

As a lot of my colleagues, my students have been struggling mightily with two digit multiplication.  Before getting to multiplying with decimals, this step usually leaves me and the students highly frustrated.  Of course this usually leads to the discussion that today's students just don't know their facts.  "In my day..." Ya, I know you had to walk uphill both ways in your bare feet, is what the students usually tell me.

Back to math, our junior intermediate divisions have decided to have a mini focus on math facts during the month of October.  The students are completing daily activities (times table challenge) and games (multiplication bingo) for prizes and 'bragging rights'.   This is having a real positive effect on our students ability to quickly manipulate single digit multiplication.

However moving to two digit multiplication, there seemed to be no carryover.  Most students were unable to transfer their knowledge of single facts to the standard multiplication algorithm.  Multiplying and carrying at the same time were proving to be a chore.  The students and I had just about given  up, when I happened across Big Ideas from Dr. Small.
She explains in detail, the lattice algorithm (pgs. 37,38) for multiplying multiple digits in a visual sense. 

The lattice system worked exceedingly well for the students.  Each digit is automatically placed in the proper place value column.  In the example above, the pink represents the ones column, the orange the tens column, and so on.

The ah-hah came after ten minutes of dissecting the strategy with the students and their applying the strategy.  We went from two students being able to multiply two digits to 15 students being able to consistently and accurately multiply two digit numbers.  The other beauty is the lattice also works as the numbers get even larger and also work for decimals as well.

I have included a link to a you tube video showing the lattice algorithm in action.  This does not mean that this is the only way to multiply, but if students are struggling with the standard algorithm, this will certainly increase their confidence and lead to increased participation during your lessons.  I actually had students that asked for homework over the holidays.  Even student mentioned that I have never understood multiplying before but this is easy!

Some student before and after samples are shown below.

I can't wait for Monday, to see how this goes with the introduction of the decimal.  Wish me luck!

P. Cornies


  1. Very interesting Paul. I had never heard of this technique before. Does this mean you have to provide extra space for tests and quizzes? :)

    1. It's actually interesting. When I gave the test only a handful of students used this method (all correctly by the way) which was disappointing. When I asked the students why they chose the standard algorithm and got it wrong, their basic response was, that is what I always use. AARRGGHHHH!

  2. This reminds me of something similar - the window method.