Dichotomous Key

To help in identifying objects like rocks, plants, animals, sea shells or other stuff, knowledgeable people create dichotomous keys.  When using these keys you answer questions about the object always beginning with number one and following the directions as you go along.  Each question should create a situation where the object fits into exactly one of the categories. Using a dichotomous key in nature studies can help kids to understand concepts like the difference between a mammal and an insect or the more subtle differences between two types of insects.  It also helps them to observe the subject closely, especially as they get into more complicated identifications.

We’ve created a very Simple Dichotomous Key for you to use with young kids up to about 4th or 5th grade.  The key includes photographs of a few living things and applies only to the specific set of images we provide with the key.  You can’t use it to identify anything out in your backyard for example.


Here’s a visual image of how a dichotomous key works:

The printable key we created is especially useful when teaching young kids about the major categories of animals: mammals, fish, reptiles, insects, spiders, amphibians, and birds.

Additional Layers

  • Having kids create their own dichotomous key for a specific set of objects (like candy or toys or pets or family members) is a great way for them to really understand how this works.  It’s also an exercise in logic as they try to create categories that will allow each object to have exactly one answer. They will also understand that objects (or plants and animals) can be grouped in more than one way.
  • The dichotomous key also gives insight into how the animal classification system works.  At each level of the classification system whole bunches of organisms are eliminated, narrowing the pool.  For example, what happens when I ask whether the animal has a backbone?  Well over half the animals are put into the non-backbone category and I can move on with a much narrowed field.  Then I might ask if it has feathers.  Everything without feathers would be shunted to the side and so on.  For the most part people take into account the way animals look and the way they behave or function when putting them into categories, though in recent years the way their DNA stacks up against other animals is taken into account as well.
  • This dichotomous key and also a more detailed one using scientific names for older kids is part of Layers of Learning Unit 3-1.

More From Layers of Learning

This exploration is part of our science curriculum, from Unit 3-1, which also includes a more advanced dichotomous key for older students.


  1. I could have sworn you’d blogged about this before, because I remember learning about this from you and I hadn’t known the name before.

    Either way, it’s still a very cool thing to learn about.

    Thanks for linking up to Science Sunday.

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