No Series: Dichotomous Key

Dichotomous Key

Lesson Objective: Use a dichotomous key to classify shoes and then apply that to cacti
Grades 2-3 / Science / Biology


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Discussion and Supporting Materials

Thought starters

  1. How does starting with shoes help students learn about using a dichotomous key?
  2. What advantages exist in having students identify plants outside instead of plants in a book?
  3. How could you adapt this lesson plan to work near your school?


  • Private message to Lisa Keyser
Interesting lesson. I hate not thought of teaching dichotomous keys before.
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  • Private message to Jessica Smith
WOW! This is an amazing lesson! I love how you made it relevant and realistic. The students probably loved feeling like they were real scientists and loved being outside studying their own environment. So impressed! Thank you for sharing these ideas!
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  • Private message to natyeria waller
Still don't know what to use
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  • Private message to M Salvona
Great Idea - thank you!!
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  • Private message to Amber Berry
I really enjoyed how you began this concept and engaged your cohort of students immediately!
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  • Great Lesson Ideas: Dichotomous Key with Caryl Crowell

    Crowell: [00:00] Hello, I’m Caryl Crowell. I teach at Borton Primary Magnet School,

    Great Lesson Ideas: Dichotomous Key with Caryl Crowell

    Crowell: [00:00] Hello, I’m Caryl Crowell. I teach at Borton Primary Magnet School, and I have a second/third grade multi-age class. [00:00:14]

    [00:00:19] Today we went out in to our Borton environmental learning lab to identify cactus. We’re working to try and figure out why the vegetation is so different from one side of the habitat to the other. In order to collect some data, we’re identifying cactus, so we were using a dichotomous key, and the children went in small groups to different parts of the habitat to use their keys to identify a cactus. [00:00:45]

    [00:00:46] I want you to find page one in your guide. Page one. Okay who’s going to read the first paragraph for us? Okay Mario, go ahead. [00:00:59]

    Child: [00:01:00] If the cactus still has stems which are flattened sideways, go to page 14 and see exactly what kind of prickly pear cactus you have. [00:01:12]

    Crowell: [00:01:13] Who will read the one on the bottom? Annalynn? [00:01:15]

    Child: [00:01:16] If the cactus you are looking at has cylinder stems go to page two. [00:01:21]

    Crowell: [00:01:21] All right, so look at this cactus, is it flattened or cylinder call? [00:01:26]

    Children: [00:01:25] Cylinder call. [00:01:26]

    Crowell: [00:01:26] What page are we going to go to? [00:01:28]

    Children: [00:01:27] Two. [00:01:28]

    Crowell: [00:01:28] Okay everybody turn to page two. [00:01:30]

    Child: [00:01:31] If the stem does have continuous [inaudible 01:35] then start to page four. [00:01:36]

    Crowell: [00:01:37] Okay. If the height of the stem is less than seven times the diameter, go to page five. What page do you think we’re going to? [00:01:44]

    Child: [00:01:45] Five. [00:01:45]

    Crowell: [00:01:45] All right, let’s move to five. [00:01:47]

    Child: [00:01:48] Go to the page 22 and see exactly what kind of barrel cactus you have. [00:01:51]

    [00:01:53] It remains [inaudible 01:54] like a fish hook, it is a fish hook barrel cactus. [00:01:57]

    Crowell: [00:01:57] Well what do you think? [00:01:58]

    Child: [00:01:58] A fish hook barrel cactus. [00:02:00]

    Crowell: [00:02:00] A fish hook barrel cactus. All right now—before we went out into the bell, the children needed to know how to use the dichotomous key and the easiest way to teach them how to do that was to actually make one. So we all took off a shoe and put them into a big pile on the floor and had to sort them into two categories. Then we worked with one category and had to sort in two categories again. Then keep sorting so there’s always two groups until you get down to one shoe per group and then you can identify the shoe. After the children had done that in the classroom, going out into the bell to use that kind of a key to identify cactus was a really easy thing for them to do. I think they caught on very quickly today. [00:02:47]

    [00:02:48] Does it not or does it have continuous ribs? [00:02:49]

    [00:02:50] We using identification, so careful observation, using a key, using the vocabulary that accompanies describing the plants that we’re looking at. Of course, you saw the kids reading, writing, using map skills so a lot of different skills involved but the focus is on the science and the question that we’re investigating. [00:03:13]

    [00:03:17] The children love being outside, and they love working like scientists. They love feeling like they’re doing something really important that matters. And they get excited when they learn new things. [00:03:27]

    [00:03:28] In order for somebody else to try this, I would encourage them to create a dichotomous key first using shoes. That’s really easy. Every child has them. It gets a little stinky, but it goes pretty quick, and it’s easy to do and fun. By constructing the key with the children, it’s easy for them to understand how a dichotomous key works. Then any kind of dichotomous key that’s available for whatever area of the country you happen to be in, can be used by kids outdoors to identify plants. [00:04:00]

    [00:04:02] The teacher can take a class outside anywhere, out onto a city street looking—there is an ecosystem in the city with squirrels and birds and even weeds growing up through the cracks in the sidewalk. Any place that there’s plants and animals, teachers can take their kids to experience outdoors, to learn about how those things interact and just about anything else they can imagine doing outside. [00:04:28]

    [00:04:30] I’m going to offer you a lesson plan for a dichotomous key with shoes. Also some suggestions for using a dichotomous key outdoors with children. [00:04:39]

School Details

Borton Primary Magnet School
700 East 22nd Street
Tucson AZ 85713
Population: 450

Data Provided By:



Caryl Crowell
English Language Arts Math Science / 2 3 / Teacher


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