I write 145 on the board and ask students:
Which number is the ones place?
Which number is the tens place?
Which number is the hundreds place?
How many ones are in a ten?
How many tens are a in hundred?
How many ones are in a hundred?
While this is not the students' first experience with numbers in the hundreds, these questions will prompt students to start thinking about place value, will give me a sense of where my students are, and will allow me to identify any holes in my students' basic place value knowledge. For students who are struggling, I may allow them to use a more concrete model (place value blocks or cubes) to help them answer the question.
We have been working a lot in our tens and ones places but today we are going to start working in our hundreds place. As we just talked about, one hundred is made up of 100 ones or 10 tens. Today we are going to talk about what happens if we add or subtract 100s from a number.
Using place value blocks (B and A groups), I build a three-digit number on the rug or underneath the document camera.
I then ask the class: What number did we build?
I add another hundred block to my model.
Turn and Talk: How can you figure out what number I have now? Share your strategy with your partner.
Have at least two students share out a strategy that they or their partner used. Students should be able to determine what number we have built based on simply counting the extra hundred. However, students might say that they simply counted the extra block, that they added ten 10s, that they counted on…’
I write the original number on the board and write the new number (100 more) underneath.
Turn and Talk: What do you notice about these two numbers?
Students should be able to recognize that the ones and tens places did not change only the hundreds place changed.
Turn and Talk: When we added 100, why did the ones and tens places stay exactly the same?
Students may note that only the hundreds change because we did not add any ones or tens.
I divide students into groups of three or four and hand each group a bag of place place value blocks (a number in the 200s or 300s). I ask students to determine in their groups what number they were given. I then ask students to make their number 100 less. I observe how students work in groups and determine how to take 100 away easily.
I ask the groups: How much do you have now? How do you know?
I then write the two numbers on the board and ask students: Why did only the hundreds place change?
Students might say "it only changes in the hundreds place because I did not take any ones or tens away" or they might say "I did not have to regroup". Push students to explain their thinking.
Depending on time, student understanding, and student engagement, do more practice problems using place value blocks.
Independent practice is tiered based on student understanding. I determine these groupings based on student understanding during the introduction to new material and guided practice as well as that students' overall holistic mathematical understanding. These independent practice groups are fluid and change from day to day.
Group A: In need of intervention:
Students will work on a worksheet with numbers 100-300 that has pictures of place value blocks. This group will also be able to use place value blocks to help them visualize what it means to take away 100.
Group B: Right on track!
Students will work on a worksheet with numbers 100-300 that uses pictures of place value blocks.
Group C: Extension:
Students will work on a worksheet using numbers 100-700 without pictures or place value blocks.
Now that we have had a chance to practice this skill, we are going to share our work in our math groups. In your math groups (A/B/C groups), I want you to share your work. You can use the following sentence stems:
I solved this problem by...
I used _______ strategy...
I checked my work by...
As students share, I circulate and listen in on student conversations, checking for student understanding and any misconceptions.
When finished, I bring the class back together and ask one student from each group to share out a problem. Encourage students to explain their strategy and to explain WHY only the hundreds place changes.