Elementary Math: 2-Digit Subtraction Lesson and Math Facts Within 20 Mastery

I like math now. I used to think I didn’t like it very much.

Since I’ve been teaching little (and big) people about math, I have come to love it like it.

2-Digit Subtraction with Regrouping

Last week, the 2nd graders and I explored 2-digit subtraction with regrouping. I had held off on this with my 2nd graders, because they haven’t achieved mastery of their addition or subtraction math facts within 20. They do know how to find the answer if they don’t know it right away, but I wanted them to be able to say the answer within seconds on every fact. It just wasn’t happening, though with time and tools (fingers, thinking, abacus, number line, etc.) they could find the correct answer.


But I realized they were beginning to dread math and … perhaps, hate it. I knew I had to make some changes. I searched within my inner teacher remembered some wise advice from a seasoned homeschool Mom who had advised me several years ago to not hold them back in math while waiting on mastery.

So we forged ahead and used a pinterest post to work on 2-digit subtraction with regrouping. They seriously grasped it within MINUTES of me explaining it. They have a solid understanding of hundreds, tens, and ones, so they grabbed onto the idea of using some of the tens to add to the ones.


After a couple of examples, I gave them each several problems to work with the LE*GO bricks. They did well.

I then gave them some to work on paper without the LE*GO manipulatives at their prompting. They aced them.

I wanted to give them this intro into 2-digit subtraction with regrouping and to record what they had learned as well, so I had them gather their math notebooks and some markers.


We used another pinterest pin to put a new page in their interactive notebooks. I encouraged them to use color to make their own entry in their notebooks, and they did so well!


After continuing to explore this concept and work out problems, I am confident they understand the concept. Now we will just work on gaining more ease and comfort as well as continuing to work on those math facts within 20, which brings me to the next set of photos.

Math Facts Within 20 Mastery


You might see in the above photo some finger counting going on … sigh. I guess on the positive side, he knows HOW to find the answer. I just am hoping by summer, they just KNOW the answer.


In a quest to continue mastering those math facts in a way that isn’t drill and kill or one and done, I have been creating a series of games and task cards with different themes. This is the latest one I’ve created with a snow theme, and they like to play it a few times a week.


After noticing the finger figuring above, I decided to pull out their notebooks and turn to the Hundreds Charts I made a couple of years ago. I encouraged them to use the chart instead of their fingers, and they made use of it I’m happy to say!


With Snow Day Take Away, I’m able to choose from one of three game boards (color AND black-and-white options) to use with the 50 task cards, which all have subtraction problems within 20. Each of the game boards differentiate with the first one giving just a number on the spaces. The second one gives the answer as an addition problem using doubles addition, a number + 0 and a number + 1. Finally, the third and hardest game board uses addition problems on the game board, but they are varying such as 7 + 6, which would match with 20 – 13 on the card or 8 + 5, which would match a card showing 19 – 6.


With each game board, the student goes to the space that has the same answer as the problem on the task card they’ve drawn.


I have also included optional play suggestions as well as a set of recording sheets for use with the cards as well for independent work.


I laminated the recording sheets (but you could use page protectors as well), so that we can reuse them again and again. I have my 2nd graders check their own work with the included answer key.



I don’t know about you, but I find varying methods for learning and mastery work best here.


In addition to these kinds of hands-on activities, my students use my iPad several times a week as well as the laptop and IXL math for math practice problems.

While all of this math learning was going on, a certain Li’l Bit was busy as can be making her very own “starflake” with the pattern blocks.



I think a certain Li’l Bit was really paying attention to our previous lesson on snowflake (or “starflake” as she calls it) symmetry!


A Question For My Readers: What do you find most helpful for mastering math facts besides worksheets, flashcards and drills?


4 thoughts on “Elementary Math: 2-Digit Subtraction Lesson and Math Facts Within 20 Mastery

  1. Hi
    I’ve been reading your blog for a long time and really enjoy it! I am a speech therapist that works in educational settings or one-on-one private language-based therapy for academics. I’ve also been a home school teacher for a non-traditional learner who is not my own child. All of that is to say, I know the challenges of math facts! Many people believe math should be easier to learn for children with language learning differences because “it’s numbers, not letters!” but you and I know that’s far from true. Math is extremely language based and becomes more so as the years go by.
    Prepare yourself: I’m going to give you a long math facts suggestion and I hope I can explain it clearly. What I have found over many years is a couple of things, although children may not always be able to verbalize it: 1. they feel overwhelmed by the quantity of math facts to learn and they feel like the facts are unrelated to each other – meaning they are all stand alones. 2. they generally do not see how each fact relates to the others or how knowing a few facts really means you know them all. It sounds like maybe this is the case with your kiddos.

    I’m certainly not telling you how to teach, but you may wish to consider some things that have worked for me. The first is a really accurate assessment of what they already know. I am always surprised when I do this!! I either have way over- or way underestimated how much the child knows. I give a simple “flashcard test”. We go through ALL possible addition (save subtraction for later) problems and sort them into 2 piles – the ones the child knows immediately vs. the ones they take time to solve. Then we have a little celebration over the ones they know quickly and their work is done and yours begins. You have to really analyze which ones they know and which they don’t know. You will begin to see some patterns and/or you will begin to see a small hole that can be quickly filled. Pull out about five or six facts that you feel like are priorities and spend time just focusing on those. I know it sounds crazy, but leave everything else behind. Once you feel like they know those five or six facts then integrate them into the group they already know. Practice what they know for a while to enjoy success then choose five or six more and proceed in the same way as before. This helps with the “too many facts to learn” perception. Once you’ve reached a “good place” (and only you know what that is) start talking about opposites (math term is: reciprocals but little ones usually already know what “opposites” means). Going forward, the concept of reciprocals is crucial so you might as well start with it now. I promise you that once they start to understand that addition is the opposite of subtraction, the skies will clear and the birds will sing and life will be good. Here’s why. If you know the addition facts and you know that addition and subtraction are opposites, then you already know all the subtraction facts, too! They are just organized differently on the paper! Example: if you know that 3 + 1 = 4 and subtraction is the opposite, then you don’t have to wonder about 4 – 1, you just think about the addition you know and think about it’s opposite. This solves the perception of the facts being unrelated. It’s slightly different from fact families, but it works. The other thing I find helpful is for kids to realllly have a firm grasp of the “ten pairs” (1 and 9, 2 and 8, 3 and 7, etc) I’ve seen that represented on your blog so I know you do it already. None of this works quickly, but you homeschool and you have all the time you need!

    Just for the future, this works for multiplication and division facts too. Focus on the multiplication, establish that division is the opposite and proceed.

    This is the longest comment in the history of comments! So sorry to take up your morning with so much reading, but maybe there’s something here that’s useful for your cuties! You are welcome to email me back if I can be more clear about something.

    • Kari, I just had a birds singing and skies clearing moment myself! This sounds exactly like what I needed to read. Math is definitely influenced by language and delays in that.

      I would love to email you. I would love a guest post by you with some Q&As related to this topic.

      THANK YOU SO MUCH for your comment and sharing your expertise.

      • Well, you’re welcome! 🙂 I am happy to help in any way I can!

        In addition to the kinds of work that I mentioned in my first comment, I teach a preschool class of 3 year olds two mornings a week. (Private therapy is not always friendly to my family schedule because so much of it happens after school hours, so I try to have most of my work happen when my daughter is at school. It’s a blend.) Anyway, I have a blog for my preschool class and you are welcome to visit it. It’s the right age group for your littlest daughter and maybe a few things you can adapt up for your second graders. The address is: http://www.learnthroughplayslc.blogspot.com. I am not looking for publicity. I don’t have ads on my blog or anything like that. In fact, feel free to keep this information for yourself!!! At its essence, the blog is a communication tool for the families in my class, but I do have some readers out in the big world. I’m simply suggesting it because you might find something there that could work in your family school. I’ll tell you right up front that it is an old fashioned, child-directed, play-based program. We are not into worksheets – we are into toys. We are NAEYC accredited and the preschool is nearly 65 years old! We meet from 9 to 12 o’clock, two days a week – only 6 hours a week. It is very unusual to find a school like ours even in a big city like mine.

        My goodness, I am chatty today! Sorry!! If you feel like it, poke around on the blog and you are welcome to contact me or ask any questions at any time!

  2. I really appreciated both the post and the above comment…but what do you do when the concept of opposites doesn’t mean a thing???. I seriously think my girl has a processing issue, along with serious lang based issues…oh, the challenges…

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