SWBAT identify bundles of 10 that add to 100

Grouping by tens reinforces the understanding of place value

10 minutes

I ask students to take out their small math journals. I put the following word problem on the board and ask students to solve it in their math journals.

*There were 18 jack-o'-lanterns on the fence. There were 22 jack-o'-lanterns on the ground. How many jack-o'-lanterns were there in all?*

I give the students a few minutes to solve the problem and then ask for a volunteer to explain how he/she solved the problem. I remind students that an answer is good, but being able to explain how they found the answer is even more important.

I ask for other students to also share how they solved the problem. We check together to see if the answer matches the problem.

I tell students that today they will be doing a counting activity that will then give them the materials to make a jack-o'-lantern face. I tell them that they will work first at their tables and then independently. I ask them to clear off their desks and then give me "hands and eyes" (an expression to mean hands folded and eyes on me.)

Today's lesson is a concrete way to look at how when we look at a number such as 35 we are really talking about 3 tens and 5 ones. Students can read the number as 35, and they may even be able to correctly pick up 3 tens blocks and 5 ones, but when asked what the 3 stands for, they say 3. The Common Core Expectations are that students will add and subtract within 100 using place value strategies. If they do not understand that the 3 in thirty 5 is really 3 tens, they will not be able to use place value strategies to support their reasoning later on. Today's lesson is taking a step back to a first grade skill to make sure that students understand what that 3 really represents.

We can't always jump in and assume that students really understand all of the things they were introduced to in first grade, and having listened to students as they try to explain what that 3 really means, I know that this is a valuable reinforcement of previous learning that will support a stronger math foundation in second grade.

30 minutes

Before the lesson begins I use an Elison press to cut out a variety of paper triangles, squares and circles. If you do not have a press, or want to do this by hand, cut paper into 4 inch squares then you can cut them in half to make rectangles, and diagonally to make triangles. You can round off edges to make circles. I lay out paper triangles, paper squares, paper circles and paper rectangles. I tell students that at each table they must collect bundles of ten of each shape. They can have more than 1 bundle of any one shape, but each shape must be collected in bundles of ten.

I give them 5 minutes to collect bundles of ten and put them in plastic baggies.

At the end of the 5 minutes I ring the bell and ask for any extra pieces to be put on the large table in the classroom. I ask each table to count how many bundles of ten they have for each shape and record it on the recording sheet.

I introduce the idea of comparison here. I show one tower of 10 cubes and another of 15 cubes. I ask how many more is in the tower of 15? As students suggest an answer, I say do I want to put the two towers together to get the answer( and I demonstrate that I would now have a tower of 25) or do I need to find the difference between the size of the two towers, and I put them next to each other again to show that they are not the same size. I do this with several other amounts so students can see that comparison is not adding (a plus problem), but subtracting, or counting back problem.

I now ask the students to create a comparison problem, comparing how many more of one shape they have than another. Each student should write their own problem on their recording sheet, using the bundles of ten on their table. They should write the problem and the answer on their own sheet.

After all of the children have completed a problem, I collect the problems and tell students I will read a few aloud and ask for the other students to figure out the answers.

I also have a challenge page that I have printed from web resources for second grade word problems for students to work on while waiting for peers to finish their word problems.

15 minutes

Students have collected the bundles of ten for the shapes. I now hand out blank orange pumpkin shapes because it is Halloween week. I tell students they may use the shapes to create awesome Jack-O-Lantern faces. (At another time of year the shapes could be used to make collages, designs, snow flakes, etc.)

I display the creations around the room after they are completed. I put the word problems up with the creations for others to attempt.

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