Doubles Plus or Minus One

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SWBAT use what they know of doubles and partners of ten to add or subtract numbers that are one more or one less

Big Idea

One of the Four Critical Areas of 2nd grade math is the application of understanding of models for addition and subtraction. An efficient way to do this is to develop strategies built on what students know.

Warm Up

10 minutes

Today I begin with a quick review of the doubles rhyme that students created in the last lesson, and the partners of ten rhyme that we have been practicing. I have typed up the doubles rhyme and add a copy to each child's notebook as a reference page.

We recite both rhymes and then I call out some mental math problems using doubles and partners of ten. 

After this review I ask, "What if I had 6 + 7 instead of 6 + 6? Is there something I already know that could help me solve this problem?" I ask several students to give their solution, reminding them I want to know how they would solve the problem, not what the answer is. 

I repeat the process with the question, "What if I had 8 + 7, instead of 8 + 8?"

I want my 2nd grade students to look for strategies to be more efficient in computations, including doubles strategies and making tens which supports the Common Core math strategies that students should be developing.

 I tell students that today I will teach them a new game using this idea of one more and one less. I bring students together at the rug to learn the game.

Playing The Game

20 minutes

Today I am going to play a game with the students and then have them play on their own. I have created game boards that are mostly just blank playing boards. The game requires cards for each team labeled +1, -1 and =, It also requires a single dice for each person and colored playing chips.

The game I teach students today is called Doubles More or Less. I tell students that they will roll one die. I use oversized foam dice to demonstrate. I roll a 4.

I ask, "What's the double of 4?" They say 8.

I tell them that now I must draw a card. If it has a +1 on it, I can move the double of 4, or 8 +1. If it has a -1 then I must move the double of 4 or 8 -1, and if it has an = sign, then I just move the double.

On the board I move my chip 7 spaces because I drew a -1. Next I ask a student to roll. We repeat the process with their roll and they move their piece on my board. We each take one more turn and I ask if everyone understands before partnering students and handing out materials. I tell students that if someone wins the game, they can play again.

I have created game boards for each team of students. Each team also has 2 colored chips, the +/-/= cards and 1 die.

I give students about 10 minutes to play the game.

Independent Practice

15 minutes

Students are given word problems to practice what they've learned. There are several sets of problems, to allow for differentiation. 

I circulate around the room, asking students how they are solving their problems. Part of the work students do is to color code their answers as double +1 or doubles -1. This keeps the focus on the new strategy learned today. 

As I listen to student thinking about their use of strategies I keep quick notes to guide my future lesson planning.


5 minutes

I choose one of the additions problems and started the problem on the board (by drawing the first number). Next I ask for a volunteer to come up draw the second number next to it. Together we looked for the doubles fact, and then I circled the one more. I asked for a volunteer to write the number sentence on the board. We talked through the problem about the doubles fact that was close to our problem, and about how our new problem was only one more. I tried to walk the students through finding the double, seeing the one more and just counting up one from the double they already knew.

It was a good opportunity to go slowly, and expand on the "toe hold" I had made when I went back to using concrete representations, step-by-step, to thinking about doubles plus one.