SWBAT use repeated addition or repeated subtraction to find the relative sizes of sea creatures.

How big is a lobster compared to a clam? Can we use relative size to find out?

10 minutes

The students are studying the ocean. They have become really interested in ocean animals, especially mollusks and crustaceans. They have learned that mollusks have a hard shell that is not part of the body. There is a soft body inside. The body has a single foot. They have found that crustaceans have a segmented body with an exoskeleton, 10 jointed legs, and 2 antenna. Students have also learned that there are mammals living in the ocean that have live babies and need to come up to the surface to breathe air.

With this background knowledge, I tell students that we are going to create an ocean mural but that we need to make sure that the animals are the right sizes. I hand out a sheet that shows the actual sizes of each of a list of sea animals.

20 minutes

I post the list of actual sizes on the Smart Board in addition to the copies that I handed each student. We read the sizes together. Now I ask students if we can make each animal its full size? Students say yes. I ask for two students to get out a measuring tool (choosing the appropriate tool on their own - MP5) and show us on the floor how big the dolphin would be. We look at how big that animal would be if we made it full size. I ask students if we might need to make the animal smaller than it really is. How would we know how big to make it?

I ask students if the map at the front of our room is full size? Why not? Does anyone know how they draw a map so it represents the real thing?

I introduce the idea of relative size if no one brings up the idea. I explain that we decide how many inches might equal 1 foot and then we use that same scale for every animal.

I explain that we are going to all use the same scale to figure out the sizes for the animals we will put on our poster. We are going to make each animal half of its regular size. I tell them that because so many of our mollusks are so small, we will use a slightly different way to decide how big to make these creatures. I give an example of how to figure out how big to make the smaller animals.

I show the students how to convert the size of one of the large animals on the list.

Now I ask students to pick a mollusk, a crustacean, a bird and a mammal from the list I have handed out. They should try to figure out the new size they will use for their drawings.

I give students a chance to finish this and then we compare the amounts we have found. We agree on how big each animal will be in relative size to one another.

30 minutes

I put out construction paper in 2 different sizes. I ask students to start with their mollusk, crustacean or bird to make their first creature of relative size. I put out rulers and tape measures. I encourage students to choose the appropriate tool and to measure the size the animal should be and then to try to draw it that size.

The children work independently to create their creatures and then glue them on the mural.

Students can begin working on a second creature if they complete a first.