Lining Up the Decimals

Adding and subtracting decimals has been a bit of a sticking point for my students.  It isn't that they don't get that you have to line up the decimals....they really do.  But when it comes down to it, they seem to be a little stuck there.  When I give them numbers such as 4.5 + 3.4, they are golden.  But when they get 12.3 + 4.52...all heck breaks loose!   And don't even think to throw a whole number in there!  OY!!

So I came up with this little "game" (that, truth be told, really isn't a game, but I called it a game and my students were hooked ;) )

I created a little game board on a piece of construction paper.  It had 3 decimal slots, a + and a line.  That is it.  Then I cut up about 15 cards and wrote decimals with varying place values on it.

On their turn, the student picked three cards.  They then lined the decimal that was on the card up with the decimal that was on the green paper.

They ended up with a math problem that looked similar to this.

Then, both partners solved the problem and checked each other.  Once that was done, they reshuffled the cards and started again.

Done and done.  And I can't tell you how much my students enjoyed it!  They also really saw how the decimals matter in the problem.

Simple, effective, and cheap :)  My kind of math game.

What do you do to help your students remember to line up the decimal?


  1. This is awesome and so easy!! We just finished up a unit adding and subtracting decimals. I will have to remember this for the future, it would be a huge help!

    We did a lot of note-taking (highlighting the decimals lined up) on this last week. :)

    1. Highlighting is a good idea :) This was actually a review lesson, as I *thought* they had it before. So maybe a few weeks down the line you can do it! Seems like our work is never ending, huh?

  2. Great idea. We'll have to give it a try. My students love sticky notes so I might have them use those. I wish I had a fun tip to share, but what we've been doing is pretty simple. They write the first number. Then they set up the problem by drawing the decimal underneath and putting the line and operation under that. They they put the decimal for the answer. After it is set up, they go back and add the second number. Having the decimal drawn first makes them pause before putting the numbers in long enough to line it up properly. Thanks for the fun suggestion.


  3. I know exactly what you mean!!! We've been doing operations with decimals as part of our number of the day every day since September, and I think this repetition seems to be helping. LOVE your idea - think I'll give it a try when we get to that unit.

    Runde's Room

  4. Hi Stephanie:
    Early in the year, I started to talking about whole Kit Kat bars and Kit Kat crumbs. When they compare numbers, some of them still say: This one is more because there are 8 whole Kit Kat bars...

    I love this handy helper. I hope it it's okay if I borrow it for Monday!

    : )
    Finding JOY in 6th Grade

  5. Fantastic idea! And this is exactly what I'm teaching right now:) I'm putting this on the lesson plans for Monday. I do have a song we sing. It is kind of an army chant about how you have to line up the soldiers (decimals). Thanks for the idea!


    1. Oh, I just thought of a way to make it into a win/lose game. Have them each draw three cards, add them together, and the one with the biggest number wins. That covers two skills, too.


  6. I love this idea and am introducing adding decimals tomorrow so thanks A TON! Selina, the win/lose idea is awesome, as well :)


Please leave a comment! I love to hear what you think about what is posted :)