Lately, I’ve been getting a lot of questions about how to teach common denominator, and I know that teaching this skill can get very tiresome quickly. All of the little opportunities for errors with making equivalent fractions, adding and subtracting, and when they think they are done, they must simplify the fraction. It can get tedious quickly. One area I have gotten close to perfecting is teaching my students to make common denominators.
How to Teach Common Denominators: Use Manipulatives to Find Equivalent Fractions
This one is pretty much self-explanatory. The students will use manipulatives, either fraction strips or an equivalent fraction chart, to convert the fractions to equivalent fractions with the same denominator. This strategy is not something they can replicate without actual manipulatives or a similar resource, but it builds the conceptual understanding that the students are finding equivalent fractions.
How to Teach Common Denominator – Find the Least Common Multiple
This is the trusty strategy that we have all learned. For this strategy, students will list out multiples for each denominator and choose the least common multiple as the denominator. I have my students list out the first five because, typically, that is all that is necessary. When I teach this strategy, I explicitly connect it to the work we did with manipulatives.
Similarly, when discussing the next two strategies, we connect back to finding the least common multiple because the next two strategies are “shortcuts” to finding a multiple and converting the fractions to equivalent fractions.
How to Teach Common Denominator: Convert Only One of the Fractions
As mentioned above, I teach this strategy and the next one after I have taught common multiple because they build upon each other. However, this is one strategy I try to get my students to use if they can because it saves so much time and leaves less room for error as they only convert one fraction. It also saves them from having to list out multiples if they can use their number sense to see if the larger denominator is a multiple of the smaller one.
For this strategy, the students examine the denominators and use what they know about the multiples to determine if they can convert the fraction with the smaller denominator into an equivalent fraction with the same denominator as the other fraction. When working with this strategy, I use this language to prompt my students: Is the larger denominator a multiple of the smaller denominator?
How to Teach Common Denominator: Multiply the Denominators
This is my least favorite strategy when it comes to how to teach common denominators, but my students love this one. I typically only teach it and address it if it comes up from the students. I don’t love this strategy because it can be seen as a trick, and students can blindly do it without understanding why and what they are doing. However, it can be incredibly helpful to some students.
For this strategy, the students multiply the denominators by each other to create equivalent fractions with the same denominator. I tell them to only do this if it gives them a denominator less than 30. Anything above 30 gets too big and complicated when they simplify their answers.
What to Do After Teaching Common Denominators
After teaching the four strategies, I will use the anchor chart to review and discuss a “strategy” for which strategy to use. About half of the chart is prepared beforehand (everything but the example work). We work on the same anchor chart for a few days (pacing depends on the students). We practice the strategies several times as a review on whiteboards before writing the example problem together on the chart and their printables. The printables stay in their math notebooks for them to reference as needed.
Need some resources to help teach common denominators? Click here to grab my 4th Grade Fractions Math Notes.
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