Sunday, January 27, 2013

The Dichotomous Key

This year is the first year I won't be the science teacher for fourth grade at our school because we switched to self-contained classrooms.  I may have said that before on here...  For someone who was never a science buff growing up, I have come to adore teaching the subject in school.  So in light of that, I'm sharing one of my favorite science units/lessons for fourth grade:  Classification: the dichotomous key.

Truth: I never knew what a dichotomous key was until I had to teach it.

When I read that part of my curriculum I immediately went to my trusty friend Google (I'm kind of a Bing girl now, but I still call it "Googling") and scrounged up every age appropriate activity and lesson I could find.  Basically, no matter which search engine you use, I have probably done every lesson it brings up.

We classified everything in sight:  shoes, buttons, monsters, jelly beans, etc.  We continued to classify until every object had it's own category.  Here are a few of our finished products:

Classifying Buttons!  We focused on using the "this/not this" format- for instance, small/not small.  It was a really hard concept for us to wrap our minds around (as seen in the following picture...small/large would not be an accurate way to set up our dichotomous key- but she caught on after that!).  

Classifying Monsters!  We did this as a class- their homework assignment was to color a monster using only yellow, red, green, and purple.  I did that just for the sake of making it easier to classify as a class.  Then we made a giant dichotomous key on the board and they each got to give a "scientific name" to their monster once he was classified to his own species.  

Flipping back through my NSTA Science & Children magazines, I ran across a great article using Jelly Belly jelly beans.  Ok, I know this isn't news in the science teaching world, but we do it every year now and it is always a hit!  Here is the article and links to the dichotomous key to use.  I don't use the "Harry Potter" version for a few reasons- one being that they are a little tricky to find now.

Students work in pairs to use their dichotomous key.  I give each pair of students 10 jelly beans.

They use copies of the NSTA dichotomous key (pink) and then fill out their key "route" to decide each jelly bean flavor.  They taste it to "confirm" that they are correct...sometimes they are not so pleasantly surprised!  

I have them draw a picture of what the jelly bean looked like next to their guess.  Click on the picture of the page for this dichotomous key freebie at my TpT store:

That's all for today!  I'm working on being better at this blog business, but for now I'm off to plan guided reading lessons for the week... a teacher's work is seriously never done!



  1. Thanks so much for the idea. I can't seem to find the pink sheet. Do you have a copy you could share with me? This seems perfect for my students. Thanks so much. :)

    1. No problem! The direct link is here -