Save the Gingerbread! - An Assessment Task on Density

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Students will be able to demonstrate their knowledge of density by constructing a model.

Big Idea

Could a well constructed raft save the gingerbread boy from being eaten by a fox? This performance assessment gives students the opportunity to find out!


10 minutes

To begin this lesson, you will need a copy of the Gingerbread Boy story.  It does not matter which one you read (there are so many available).  It only matters that the Gingerbread Boy gets eaten by the fox (or wolf-depending on your version). 

I begin the lesson by reading the story to the students.  When we are done reading the story, I ask the students a few questions to set the stage for our assessment activity.  I want the students to start thinking about the problem that the gingerbread had a possible solution for that problem.

Why did the Gingerbread Boy have to get a ride?

Why couldn't he swim across the river?  Why wouldn't he float?

What might have saved the Gingerbread Boy? 

Have you ever heard of a raft?- if there is no explanation, I explain to the students what a raft is.

We have learned a lot about density and why things float and sink.  We are going to use that information to try to save the gingerbread boy.  Let's go back to our tables and find out more about what we are going to do today. 


25 minutes

Materials Needed for Work Station (one station shared by entire class)

  • construction paper
  • laminated paper
  • cardboard
  • straws
  • small pieces of sponge
  • small plastic zipper bag (the kind used for crafts and jewelry)
  • staplers
  • rubberbands
  • masking tape


Materials Needed for Each Work Group

  • one pan of water
  • 1 gingerbread cookie or a construction paper gingerbread


This lesson will give the students a chance to participate in the engineering and design process. The students will be given a problem to solve (saving the gingerbread). They will need to design a device (the raft) and test it to see if it will float. They will be given the opportunity to make adjustments to their raft and retest it.

I introduce the activity to the students by saying, At each of your tables is a gingerbread boy.  You are going to try to save this gingerbread boy from getting eaten or from falling in the river by designing and building a raft for him.  You will be able to use any materials you want from the work station. Just take them back to your table to work with them. Make sure that when you are selecting materials, you think about whether they will float or not.  Think about the density of the items.  You have learned about density, now I want you to show me what YOU know about it thought the construction of your raft.  The raft will need to hold your gingerbread boy and it must stay floating for 2 minutes.  If it can float for two minutes in the pan of water, your design will be considered successful.

You will get the opportunity to test the raft in your water and make adjustments as needed. You will have 20 minutes to design your raft. At the end of 20 minutes, we will have the final test to see if you were successful.

The students begin working (see video) and I circulate among them observing their work.  I have a class list with room for recording my observations. I am especially watching for the students using vocabulary and demonstrating knowledge of what they have learned about density, sinking and floating and making note of this.

At the end of 20 minutes, I call the class together and we begin our final test.

The Test

5 minutes

Twenty minutes are up and now it is time to test the rafts. We move all four pans of water together at one table and the students gather around the table. I have one student from each group in front of their pan of water, holding the raft with the gingerbread cookie on it. We count off and the students place the rafts in the water. I have the timer set for one minute and we watch to see whether the rafts float or sink.

While we are watching, I engage the students in conversation about what is working or not working with each raft (see video).

At the end of one minute, we stop the test and then we examine the successful rafts.


10 minutes

To wrap up our learning, we discuss the elements that were included in the successful rafts. We talk about what elements floated and why. I want the students to make connections to each item and its density.  We then look at the unsuccessful rafts and talk about what kind of adjustments could be made to make them successful. This will lead into our next lesson in which the students will get the opportunity to make adjustment to their existing raft to get it to float.  To aid the discussion, I ask the following questions:

What worked well in the rafts we observed?

What didn't work well?

Why didn't it work well?

What are some ways that you can counter these things?

Tomorrow, you will be given the opportunity to make adjustment to your raft.  What type of changes do you want to make.

To wrap up the lesson, I give the students time to talk about what they will do to improve their rafts during our next lesson.