Piggy Bank Equations and Cross Outs

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SWBAT show the connection between counters and X's for crossing out pictures to subtract.

Big Idea

We bridge the concrete (counters) and representational (pictures) and X's to "cross out" in this important step in subtraction.

Attention Grabber/Introduction

10 minutes

Our read-aloud story after lunch Is Alexander, Who Used to Be Rich Last Sunday.

After we talk briefly about the story, including spending money, I project a mini piggy bank mat up on “the big screen.” “Remember this, friends?” I ask.

Immediately, I hear sounds of “Oo,” and a fun comment, “More money! Cool!” The kiddos just loved practicing with the plastic pennies yesterday, and we are excited to do more practice!

Guided Practice

40 minutes

We briefly do a practice subtraction story about our helper of the day to “warm up” with our mini piggy bank mats.

“Girls and boys,” I announce with hushed excitement, “I think we are ready to write some subtraction number sentences!”  Students cheer. (Yes, they really cheer… it’s all about the presentation, I tell ya!)

My helper passes out Piggy Bank Subtraction recording sheets, again found with Mrs. Ricca’s fantastic, free subtraction resources. Our mini Piggy Bank mats are right next to us we begin our subtraction practice, so we still have our concrete pennies for counting & moving—modeling subtraction (MP.5), but we now have a space to show our work with numbers, as well (MP.2). As we set up our first problem, starring the helper of the day, we put the starting amount of pennies in the bank. Then we immediately record the initial number on the Piggy Bank Subtraction recording sheet. Next, the subtraction story continues, and we state that the helper gives away 1 penny. We move 1 penny out of the piggy bank, and immediately write a 1 after the minus sign.

I interject to point out the minus sign, stressing the vocabulary “take away” and even “minus,” (which to be honest, some students have been mentioning during our whole group introduction lessons with the finger plays and math mats).

I do a silly, quick vocab check that the students have come to love: in pep rally form, I say, “Take away means—“ and students say, “Minus!” I repeat, “Take away means—“ with student response, “Minus!” Then quickly, I ask a few students, beginning with a confident student, and ending with a student who has much less academic background, but the same thing, “Take away means—“ with the single student saying (and smiling), “Minus.” We repeat this exchange quickly, sometimes whispering or saying it in a silly voice, but we practice the key vocabulary.

Moving along with the equation, I model writing a “1” in the second position (the subtrahend, for all you math heads out there!), and I stress that this is the “take away part”—only after the minus sign is where we write the part that we are moving out, or taking away. (Students will potentially have HUGE confusions in this area if it isn’t well established, practiced, and understood from the get-go, I have found!)

I explain to students, “So if the minus sign means take away, this is where we write what we are taking away! Take away WHAT?” I ask.

Students joyfully answer, “1!”

“How do I know this?” I persist—really pushing the kids, as we are really just beginning subtraction equations.

At first, I don’t pick kids with their hands raised. This ensures that all kids are participating and I’m getting a good feel for understanding among the entire group—not just the top 30%. A kiddo responds, “The 1 is after the take-away.”

I validate the student’s answer, ever-so-slightly refining vocabulary, “Yes, the 1 is after the minus sign, excellent! Thanks!”

“But how does that go with the little pennies? What part of moving the pennies are we talking about?” I persist.

Blank faces. The look every teacher, from kindergarten to college, dreads. I go back to “the big screen,” and I re-show the moving of the one penny out, without actually using any words.

“Oh! I get it! I know! I know!” I hear from around the room.

I let the kiddos explain how the “1” in the second position—after the minus sign—and again, we stress precise vocabulary in a gentle, kindergarten way (MP.6)—is the 1 penny that was moved out of the piggy bank. I ask a few students to quickly re-state this concept as well, insuring participation, input, and concept development.

Now, I go to the “top 30,” the “quick study kids” who either catch on quickly or have been working on subtraction with their families for a while.  “So now what? What do I do?” I ask.

“You count what’s left over in your piggy bank—what’s still there!” a learner explains.

After affirming & repeating the correct response, I use “the big screen” to show again the group to which we are referring. Then quickly, I move around to make sure students are pointing to their remaining 4 pennies and writing the number in the difference spot. We don’t really stress the term difference so much, as we will get to it more in later lessons. For kids who are ready, “difference” is mentioned (just not elaborated on).

We repeat this procedure several times. I make sure to circulate the room like crazy, hover only to clear up any confusions, but keeping myself on the move so that all learners are getting this critical concept. Things look great!

Next, we move on to part 2, or side 2 of the recording sheet. I made this side myself, so it’s useful, but not super cute.

As we transition, I say, “What if we’re just talking about your piggy banks, but you don’t actually have any pennies with you? What if we are talking about your piggy banks, but we’re not actually moving the pennies? Can we do subtraction without the stuff?”

I love when kindergartners first hear this question. The answer I hear at first is often, “No!”

“What if there’s a way we can show the pennies—with pictures or even those numbers we were just writing—we could represent your pennies, but not make you take them with you every time you want to practice subtracting—or taking away—pennies?” I mention, directly referring to MP.2.

Some of my top turkeys know where I’m going—they’re totally with me on the transition. All of the kids are interested. A few kids seem perplexed. We push on.

I tell the kids to flip over their recording sheets. “Penny pictures! I knew it!” some of them declare.

We directly match the plastic pennies to the penny pictures, the concrete to the representational, helping even the least experience learner make the connection between concrete & pictures. We even have numbers on the side! Whoa! (MP.2)

For the first problem, we actually model with our plastic pennies and then directly crossing out the picture pennies to match the equation over on the side. We say both “minus” and “equals” as we practice, and again, I am moving all over the classroom, hovering as needed to ask guiding questions when kids are confused.

After 2 or 3 problems, I take away the plastic pennies. We practice a couple of questions, simply crossing out the pennies to show “take away” or “minus,” and I have the kiddos do the last few questions independently, so I can get a quick comprehension check to see “where we’re at.” We are making progress with our subtraction!


5 minutes

There’s a lot to talk about today. It was a big day for math, I stress, and students nod in serious agreement. The mood is lightened quickly when one of my turkeys says, “Ms. Novelli, you took away my money!”

We all laugh, and I say with a smile, “Yes I did! And I gave you X’s!”

We discuss favorite parts of the lesson, tricky parts, key terms like “minus,” and any tricky parts of this big kid subtraction, as well, Students know their input is valued, and we agree as a group to get more cross out practice.

“Can we practice it more tomorrow?!” a student asks, in anticipation. Yep, we are hooked on subtraction!