Lesson: Tricked Out Tree Houses

Evaluate and communicate how criteria inform tree house design.

• Ask: Imagine you wanted to spend a beautiful afternoon in a tree house. What would the tree house need to have? (sturdy floor, guard rails, stairs, etc.) What would your tree house need if it were a snowy, stormy afternoon? (things to keep you warm and dry, like airtight walls) What if your family wanted to spend a week in the tree house? (food and water, lights, plumbing, etc.) Why did your list change? (the situation changed) Explain that when the situation changes, a project’s criteria—the standards by which its success is judged—changes as well. 

Preview images and read a story about tree house construction.

• Allow students to preview the images and other text features in the article. Read the article aloud. Ask: What force exerts a downward pull on a tree house? (gravity) What do designers do to keep gravity from pulling a tree house to the ground? (They choose large, rot-free trees with deep roots. They attach the platform to the trees using strong bolts.)
• Have students cement their understanding with a Quick Quiz. 

Sequence events and discuss the importance of following a process.

• Explain that engineering projects have criteria as well as constraints, or limits—for instance, how much money can be spent. Ask: When should a designer determine criteria and constraints? (at the beginning) Does the order of the steps matter? (Yes, because if you build the parts for a tree house before you pick the trees, the parts might be the wrong size.) 
• Have students complete the What’s the Order? sequencing activity in pairs and discuss as a class.

Investigate the diameter of trees in their neighborhood or near their school.

• Invite students to complete a Learning Extension, found at the end of the online scrollable article, where they measure and record the diameter of different trees. Would any of those trees safely support a treehouse? Why or why not?

Determine criteria and constraints before designing a tree house.

• Share the slideshow “Tree House Tours.” Encourage students to think about how the tree houses were built.
• Preview the Design a Tree Hideout engineering challenge as a class. Remind students why the order of steps is important, and why knowing the criteria and constraints for a successful design are important. If needed, support students in adding criteria and constraints on the design challenge. 
• Have students present their initial designs (Step 3 on the skills sheet) in small groups. Final designs can be displayed as a socially distanced gallery walk. Let students share feedback and revise their designs. 

⇨ Learning Extension: With a trusted adult, go for a walk. Bring a ruler, a very long string, and materials so that you can record data. Find a tree and use the string to measure all the way around it. Arrange the string in a circle on a flat surface and use the ruler to find the diameter. Repeat on other trees until you have 5 to 10 measurements. How many of the trees had a diameter large enough (at least 30 centimeters) to be considered for a tree house?