By Cheryl Cowan’s Third-Grade Students, Mayflower Mill School, Lafayette, Indiana
Editor’s Note: Originally published in Dragonfly Magazine in the late 1990s, this investigation reminds us that the best science starts by testing the things we think we know.

Our Spark
When we started our tree unit, we looked at the pictures in our textbook. Based on the photos, we made some predictions about the woods behind our school. We thought:
- Trees have the same kind of bark.
- Bark is very thin.
- The bigger the tree, the older it is.
How We Investigated
We went outside to prove our predictions. We each chose a tree and made “rubbings” by putting paper over the bark and coloring with crayons. We also looked at “tree cookies” (slices of tree trunks) to count the rings.
What We Found
We were wrong about almost everything!
- Bark is Different: Our rubbings showed lines that were totally different—some close together, some far apart. They felt and smelled different, too.
- Bark Can Be Thick: Some bark was much thicker than we predicted.
- Size Doesn’t Equal Age: We found a big tree cookie that had 44 rings, but another one near the same size only had 24 rings. You can’t always tell a tree’s age just by looking at its size.
GO WILD: YOUR TURN
- The Challenge: Test your own assumptions. Head to a park with crayons and paper.
- The Method: Make bark rubbings of three different trees.
- The Question: Can you match the rubbing to the tree later just by looking at the pattern? Is the roughest bark always on the biggest tree?
THE FIELD GUIDE (For Educators)
Subject: Biology / Botany
Grade Level: K–5 Inquiry Focus: Observation, Pattern Recognition, Hypothesis Testing.
The Science Behind It: Bark acts as the protective skin of the tree, and its texture varies by species due to growth patterns and function (protection from fire, insects, or drying out). The “tree cookie” observation introduces dendrochronology. Growth rings vary in width based on annual rainfall and sunlight, which explains why size does not always correlate perfectly with age.
Standards Connection:
- NGSS: Inheritance of Traits (LS3.A), Variation of Traits (LS3.B).
- Skill: Engaging in Argument from Evidence.
Materials Needed: Paper, crayons (peeled), magnifying glasses, tree cross-sections (if available).


