Dichotomous Key

 Dichotomous Key

One of the things we teach seventh graders in Texas is how to use a Dichotomous Key. We also provide them with a chance to create a Dichotomous Key because what better way to understand something than to create it.

Prior to creating a Dichotomous Key we have the students work with several of varying difficulty. My colleagues and I have located one with aliens, one with little creatures like gremlins and one that is emojis and we also use a leaf key which is scientifically inclined. We copy them so there are 2 keys per page and create a little booklet where the keys are in order from easiest to most difficult. I normally practice part of the first one with the students and then I go over the scientific one together as a class and we work the final key together. This normally takes only one and a half 45 minute class periods to complete.

Next we move on to creating a Dichotomous Key. For my regular education classes I begin with the worksheet shown above. We work on the first three sections together as a class and then I have them work on the rest with their partners. This takes up the other half a class period from the previous day.

This year I tried something new with my Pre-AP classes. Rather than begin the creation process with the worksheet I decided to begin with  a hands on activity. As a class we reviewed the Dichotomous Key creation guidelines in their notes, then I provided the students with a baggie that help 9 pieces of uncooked pasta in 3 different colors. I then encourage the students to remove the pasta from the bag and to physically separate the pasta into groups. Since there are 9 pieces of pasta and 3 colors their first instinct is to split the pasta into 3 groups by either pasta type or pasta color. This causes them to pause and really think about how they can separate them into 2 groups to comply with the options available on each section of the key.

This activity gives them a really good opportunity to truly break down the process and consider how it works. The other thing that works well in this activity is having the students work together because they do not always agree with one another about how the groups should be split so then we are able to have a conversation about how this can occur in the real world and how scientists might have to deal with these things. 

I have heard of doing this same type of activity with 15 bean soup although I think that might work better for older students. You could also make this simpler by using pasta that is only one color so the students only group them by size or shape or you could simplify the activity by using pasta that splits evenly in half each time like using small, medium and large macaroni and small, medium and large shells.

Once I have completed this activity I give the partners a worksheet with 10 creatures, they must color and name the creatures and then they must create their own Dichotomous Key. I encourage them to cut the creatures out and physically separate them into groups. The physical separation seems to help the students with the Dichotomous Key creation. I allow the student groups 2 class days to use to complete their assignment.

All in all I use a week of class time to take notes, practice using the key, and then practice creating a key.