Similarity

I have a third of my 6th graders again next year as 7th graders.  In those two years, my goal is to teach them the 6th, 7th, and 8th grade standards.  It’s been somewhat of a slow process, but I’m making progress.

This year I was able to get a unit in on similarity at the end of the year with my 6th graders.  I definitely pushed them and challenged them in this unit, and my students rose to the challenge.  I was so proud of them for the challenging proportions they were solving.  Some of my students definitely noticed that I was pushing them a bit more and became frustrated that it wasn’t coming as easy to them, which wasn’t a bad thing.  We worked through that.


It had been a while since we had solved proportions, so I started the first day of our unit with a few review problems.  I knew I wanted to use Marcellus the Giant from Desmos at some point in the unit.  As I was planning, I wasn’t quite sure when I wanted to fit this in.  Should I intro with this and have them try it without telling them anything about similarity or scale?  Do I use it after we have talked a bit about both of these?  I ended up deciding to use it right away at the beginning and was glad I did.  Students may have been confused at some points throughout the activity, but by the end they were able to explain what it meant for a giant to be scale or not scale.

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After a couple days of notes on similar polygons and scale, we did this activity around the room.  I had done another Math Lib activity earlier in the year, and my students love it.  I fully admit that I could have created something, but I was end-of-the-year teacher tired and decided it was worth it to get the activity linked above.

The weather in Minnesota was FINALLY nice, so I decided to do this activity outside with students.

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Then I saw this and knew I had to make this happen in my classroom.

Lisa used the game Clue and incorporated scale factors into the activity for students to figure out who was intentionally making math mistakes.  😉  Read Lisa’s post on how she set up the activity with her students.

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I ended up doing it slightly different than how Lisa described in her post.  I printed out Clue boards that Lisa shared and the Clue cards.  I wrote different numbers on all of the cards.

Students started by finding the area of each of the rooms on the clue board.  Once they had done that I gave them one Clue card with a scale factor on it and had them pick which room to use that scale factor for.  After they found the new area, I checked their work.

Nearly every group did what I expected them to do.  They took the area and multiplied it by the scale factor, rather than multiplying by the scale factor squared.  That was one of my main reasons for doing this activity -I wanted students to see how scale affected area since prior to this we had just talked about how scale affected length.IMG_7592

I let students struggle with that for a little bit before giving them a hint to help them out.  I put a grid up on the board and we looked at a 1×1 square.  Then I picked an easy scale factor, I think it was 2, and we talked about what the new dimensions of the square would be.  Then I asked students what the new area of the square would be?  I saw the lightbulbs go off for some students, and then I asked how that would apply to the problem they were working on.  It was enough for all groups to eventually figure out what to do in the Clue activity.

In the future when I do this, I would be more intentional about the numbers that I picked for the scale.  I used some pretty small numbers for some of the cards so after applying the scale factor the areas of the rooms were pretty unrealistic.  Overall though, it was a great activity and I am looking forward to using it again next year.

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