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A collection of helpful articles on teachers and teaching

The Power of Percentages

In math the “to die for” concept has to be percentages. I have not found the one concept in science yet but if I work in percentages there seems to be a huge pile of advantages for my students that follow. So, we are going to talk percentages all year.

The percent that the stock market is down is scrolling across my news feed right now, the weather forecast just gave me a 30% chance of rain today and I am about 50% through my to do list. We live in a world of percentages. Having a conceptual idea of percentages and being able to use them in science gives students a clear path to other data analysis tools. How to get all students to that level of understanding (where they can use the concept in diverse settings) involves some visual and tactile helps for me.
This week my students will be counting and weighing beans. This sounds like we should be studying the gas laws…not quite. Beans are cheap, easy to find and provide a visual picture of what 10%, 20% and 80% might look like. I like to use two different colors of beans. Our store had light tan beans (they call them navy beans) and some dark brown pinto beans. Putting 100 beans on the table (and you can do this by mass) then taking out 20 and replacing them with 20 different colored beans gives students a chance to look at what 20% is visually. You can do the same with any percentage of beans. After some experience with the beans and percentages try to put a mix of beans on the table and let the kids guess what percentage is the lighter color. This is not as easy as it sounds and checking the guess becomes the sticky part. With middle school students they will count all the beans into separate groups. Then, since the total number is not 100 they may ask how to figure the percentage. This is a great time to present the math of calculating percentages. The students are interested, they have a clear visual in front of them and the stage is set. This gives students the power to solve ratio problems from all sorts of applications. 

You could use dominoes, leggos, beads or anything to teach percentages. Online there are templates that are printable to use.

In science we go beyond the numbers and calculations into the use of the number. You might be talking the percent of rainfall (vs. the amount in a normal year). You might use this when talking about the amount of material that gets recycled, how efficient your car is in fuel mileage, the amount of sugar in your soda or even pollution percentages. In science we often use percentage error (how far off from the true value is your experimental result).

We often talk about percentages when we talk about water quality. How pure should our water be? If our water contains 1% of a known harmful chemical that is way too high. So, we use parts per million and parts per billion. These are very abstract numbers to most kids but the door to understanding these is percentages. A simple understanding will lead to some confusion when the students get to much larger or much smaller numbers. But, if the students have multiple experiences with percentages and a good amount of number sense (developed with the tactile and visual methods) the idea of parts per million is not a far reach cognitively.

So, I will pick up a couple of bags of beans and launch in to an easy lesson with some rich payoffs. You can use the beans to do some interesting mass calculations later in the year. I use beans to teach about isotopes and even moles. That is fodder for another blog post.

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