By the Fourth-Grade Class of Linda Slager, Stewart Elementary School, Oxford, Ohio
Editor’s Note: Originally published in Dragonfly Magazine in the late 1990s, this student inquiry explores the engineering marvels of the ocean. After seeing how corals live side-by-side in shared skeletons, these fourth graders decided to test the limits of structural design themselves.
The Spark
After a slide show on ocean corals, our class was left wondering about many things. We learned that corals live side-by-side, sharing a common skeleton. This made us curious: are coral colonies like bee colonies? Do differently shaped skeletons provide different numbers of “little houses” for the creatures inside? Most importantly, what shapes make the sturdiest structures?
The Prediction
We decided to find out by building our own “colonies” out of index cards and tape. We predicted that the greatest number of creatures would fit into square- or rectangular-shaped units. We also predicted that the sturdiest skeletons would be broad and squarish in shape.
How We Investigated
Each group received 200 standard index cards, a piece of poster board for a base, and tape. Our challenge was to design a skeletal home that could hold as many creatures as possible while remaining strong. We each planned our designs first and then started building.
The groups took very different approaches:
- Group A created triangles that fit together like a honeycomb.
- Group B folded cards into rectangular tubes and stacked them in a diamond, stair-stepped pyramid.
- Group C built a four-story cross-shaped colony with a single entrance and exit for protection.
- Group D focused on a dome shape with a base broader than the top for maximum sturdiness.
- Group E used whole, unfolded cards for the sides of each “house”.
What We Found
Our predictions were right! A broad, square, or rectangular shape was the sturdiest. We also found that little square or rectangular units created the most “homes”.
Group B was very successful because their structure was short and had a broad base. In contrast, Group E had the least sturdy structure and the fewest spaces because they used whole, unfolded cards. We discovered that groups who folded their cards and made compact units created more living spaces and stronger structures.
The coolest part was seeing how different every “skeleton” looked. It helped us understand why real coral skeletons have so many different shapes even though they all do the same job: housing tiny, soft-bodied animals.
Go Wild: Your Turn!
Can you build a better colony?
- The Challenge: Grab a stack of index cards and some tape. Try to build a structure that is at least three stories high and has at least 50 “rooms.”
- Test the Strength: Once it’s built, see if it can support the weight of a small book.
- Analyze: Did folding the cards make a difference? Which shape—triangles, squares, or circles—felt the strongest?
The Field Guide (For Educators)
Subject/Grade Level: Physical Science / Engineering (Grades 3–6)
Inquiry Focus: Structural Engineering, Geometry, and Biological Analogies.
The Science Behind It: Corals are colonial organisms that secrete calcium carbonate to form a hard exoskeleton. This study demonstrates the engineering principle that “form follows function.” In both coral reefs and human-made structures, broad bases and interconnected geometric units (like honeycombs or triangles) distribute weight and stress more effectively than tall, thin structures.
Standards Connection:
- NGSS 3-5-ETS1-1: Define a simple design problem reflecting a need or a want that includes specified criteria for success.
- NGSS LS1.A: Structure and Function.
Materials Needed:
- 3×5″ Index cards (approx. 200 per group)
- Transparent tape
- Poster board for bases
- Small figurines or counters (to represent “creatures”)