Estimating & Measuring Weight

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Objective

SWBAT estimate and measure the weight of grocery store products.

Big Idea

In order to further develop students' understanding of measurement units, it is important to provide students with opportunities to estimate and measure the weight of items.

Opening

15 minutes

To connect this lesson with yesterday's lesson, Day 6: What's an Ounce?, I began by asking: What did learn about an ounce yesterday? Students responded, "That an ounce would be used to weigh an apple." "One clay ball equals an ounce." "It takes 16 ounces or clay balls to get to a pound." Good! I'm glad you mentioned a pound! I held up the examples of 1 ounce (one clay ball) and 16 ounces (16 clay balls): One Ounce vs One PoundDoes everyone remember yesterday when we were talking about the two systems of measurement: Metric and US Customary? We talked about how grams and ounces are not equal, but you would use both grams and ounces to weigh one apple. What about a bunch of apples? What metric unit would you use? "A kilogram!" What customary unit would you use to weigh a bunch of apples? "A pound!" One student asked, "But how many pounds are in a kilogram?" I asked him to look this up on the internet! 

Meanwhile, I continued on. I wanted to help students understand the importance of understanding ounces in real life. Being able to connect mathematics to everyday life is a part of Math Practice 4: Model with Mathematics. I held up a box of Rice Krispies and explained: Fourth graders, who goes shopping at the grocery store with your parents? Whenever I go shopping, I always try to find the best deal for my money. For example, if I wanted to buy a box of Rice Krispies, I would look at the different sizes of boxes that I could buy. I showed students two Different Sizes of Rice Krispies Boxes that I had printed prior to the lesson. If I had more time, I would have given copies to each group and I would have asked them to draw conclusions about the size of a boxed product and the cost per ounce. Instead, I pointed to the Value Size Box and asked: Does anyone's family buy value sized boxes? One student raised his hand and said, "We always buy the bigger box because I have a big family." Which box do you think is a better deal? A small box of Rice Krispies or a big box? One student said, "The big box is always a better deal." Another student said, "Not always!" I then explained that I calculated the price per ounce of each box by dividing the cost by the number of ounces. I didn't explain this in detail as I wanted to focus on the purpose of the lesson. I held up a one ounce Bag of Rice Krispies and demonstrated how it was equal to a one-ounce clay ball from the day before by using a balance scale. I then explained: When you buy a small box of Rice Krispies, you are paying $0.25 per ounce and when you buy a large box of Rice Krisipies, you are paying $0.16 per ounce. Students were astonished that we pay up to $0.25 for only an ounce of cereal! I then asked students to Turn & Talk: Explain why you should care about the amount of ounces you are getting when you buy a product! I loved hearing students put this into their own words, "It needs to be fair." "You need to make sure you're not getting ripped off." "You need to get the best deal." 

At this point, the student looking up the conversion between pounds and kilograms we ready to share what he found: Kilograms to Pounds Conversion. He shared his findings with the rest of the class. Regularly using computers in the classroom supports Math Practice 5: Use appropriate tools (including technological tools) strategically. 

Teacher Demonstration

20 minutes

Students were ready to hear about the Grocery Mart drawing on the board! I simply projected clipart from my computer and traced around it, hoping to help make this lesson come alive! Again, by applying math to an everyday scenario, students learn the importance of math in real life (Math Practice 4). 

I also brought in about ten grocery store products and lined them up on the ledge of the white board: Food Mart & Products. I began by saying: Today, you get to go to the grocery store! Students responded with big smiles and comments like, "This will be fun!" I then asked students to write the goal in their journals: Today's goal is to estimate and measure the weight of grocery store products. Here's what you get to do! You get to use your knowledge of an ounce to estimate the number of ounces each of these products weigh! I pointed to the line of up products I dug out of my pantry at home. I showed students how I had covered the weight up with a blue piece of tape and explained: After each student in your group has estimated the weight of the product, you can take the tape off to see the actual weight. You can also use the digital scales around the room if you'd like! To track you're findings today, please make a three-column chart in your math journals. I modeled how to create the chart: Three Column Chart. The first column was titled "Product," the second column, "Estimated Weight," and the third column, "Actual Weight." Here, I have a Pop Tart. I modeled how to write the product name in the first column and asked students to do the the same in their journals. Please write down the estimated ounces of the Pop Tart. Who would like to share their estimate? One student said, "3 ounces!" I modeled how to write the estimate in the second column. Then I asked, How would we figure out the actual weight? Students said, "Weigh it!" I placed the Pop Tart on the scale and announced, "1.83 ounces." We wrote this measurement in the third column. For fun, I asked students: What if I crumble this Pop Tart up? I crushed the poor Pop Tart in the bag. Will it weigh less? Many students thought it would! I then placed the Pop Tart back on the scale. To students' amazement, it still weighed the same!  

Student Practice

30 minutes

Students were more than ready to begin investigating on their own! In my classroom, I always have students' desks placed in groups to make collaborative learning practical and easy to implement. I regularly ask students to work in groups to support Math Practice 3: Construct viable arguments and critique the reasoning of others. To start students off, I asked my weekly-assigned team leaders to grab a product from the board and begin! 

During this time, I walked from group to group to observe students learning. My goal was to reinforce key concepts and to identify student misconceptions. I tried to provide on-the-spot interventions through questioning and modeling.  

In this video, you'll see students excitedly revealing the actual weight of a Hersey's bar: Revealing Actual Weight. Other students used one of the digital scales throughout the room to check the weight. 

In this video, Measuring Products, students compare their estimated weights to the actual weight. I encouraged the students to grab a few green one-ounce balls from yesterday's lesson to connect new knowledge with prior learning and to help students apply their understanding of a ounce to this activity. Later in the activity, I reconnect with this group and find that they have gathered three one ounce balls to help with estimating: Comparing One Ounce Balls. I loved watching how eager the students were to place their hands on these products! 

Here, I used Questioning to push this student's thinking. Even this short conference was somewhat challenging as she was so focused on the activity at hand. She was more interested in interacting with these products than talking to me! 

 

 

Closing

10 minutes

To bring closure to the lesson, I first asked students to put all of the products back and sit down in their seats as I counted down from 10. I then asked students to turn and talk about two questions:

1. Were you surprised by any of the products' weights?

2. How will this lesson help you in real life?

In this video, a student responds to both of the questions: Real Life Application.