#13 – How we use a 30cm ruler to check student understanding (in unit conversions)

As a teacher, it’s important for me to check student understanding, to know how a student is getting an answer to a question. For a student to just get an answer to a question is not enough. What if the answer is wrong? How, then, can I help the student if I don’t even know where the problem is?


We can teach students how to solve a particular problem, how to set up a question, but unless students are actually using the scaffolds we provide for them, they aren’t really using what we are giving them. So, how do we check student understanding?


Using Simple Tools, Complex tasks to Check Student Understanding

The answer is simple: we ask students to document their process when they are solving an open-ended, complex problem. Yes, this solution appears obvious. However, my ah-ha moment only came recently, when I changed a small Measuring activity I normally do when teaching students to use unit conversions in real life. To check student understanding, students had to not just give me their answer but explain how they got their answer in the extra space provided. The explanation can be in words and can also include sketches and calculations. In fact, some of the best explanations tend to include all three. This change – providing some extra space to write down an explanation – allowed me to see who was thinking about the problem and who was struggling (or just being lazy about their explanations). And the results were awesome. If you want a copy of the of this activity, you can download it at the end of this post.


Measuring without touching

In our measuring lab, students need to find the lengths of different distances using just a regular, 30-cm ruler. For example, using only a 30cm ruler, students find the distance down a hallway (or around our wing of the school) and the height of the school building (by observing the building from a distance).


Finding the length of a hallway is usually pretty easy for students. They normally measure the length of a single tile and then count how many tiles stretch down the hallway. This is meant as a primer for students. They learn to break down a length into smaller parts that can then be counted and summed up to find the total length. My stronger students not only know to count tiles but also document their conversions from tiles to cm in the space provided. That’s exactly what this exercise is meant to practice: the use of unit conversions in real life. Those who did not write down their conversions I was able to speak with.


Finding the height of the school is a little more difficult since students are only allowed to view the side of the building from my windows (ie. They are not allowed to go up to the building and touch it). However, the previous method of breaking down the side of the building into measurable parts and then adding up those parts can be used in this question. Since windows in a building are usually the same, students can measure the height of the window they are peering through. Then, they can use it as a reference to find other lengths and heights. Again, students who understood this concept were able to document it while those who struggled I was able to connect with.


Field Notes

  • Students in our class do this activity in groups of 3 or less.
  • Stress that students can only use a 30cm ruler. No metre sticks. No protractors. Just a ruler.
  • Re-emphasize to students that they must document their process. It is not good enough to just provide the answer. One group of students in my class wrote “By visual inspection” for their documentation. I had them clarify and show their reasoning in greater detail.


Wrap Up

How do you check student understanding? How do you know students are using the tools you are teaching them? We need to ask them to explain themselves, to tell us not just what they know, but how they know it. Our unit conversion lab is an activity that uses simple tools to solve a seemingly difficult problem. Having students document their process will show which students need help and which students have a firm grasp. Because, at the end of the day, we want students to learn how to problem solve – not just learn formulas. If you want a copy of our unit conversion activity, please click the link below and join our email list. We will email the activity to you.


To download our Small Tool, Great Distances Activity, Click Here


Until next time, keep it REAL.

Posted on September 20, 2017 in Strategies

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