I go back and forth on which method I like better for finding GCF and LCM. Sometimes I think the ladder method (or upside down birthday cake method) is the best and other times I just really like making prime factor trees. There's something really cool about every number breaking down to its own, unique string of prime numbers.

This word wall reference (part of my math resource library) supports students breaking numbers down into their prime factors through the example of prime factoring the number 60 into 2 2 3 5.

The ladder method for finding GCF and LCM |

Then there's the ladder method. Some also call this the birthday cake method. I especially like this method for finding LCM because the numbers line up so nicely. One warning though: this method doesn't work so great with 3 numbers. A workaround when working with 3 numbers is to find LCM and GCF of 2 of the numbers, then use the result to find GCF/LCM with the 3rd number. The reference above is also part of my math resource library. It's also part of my 6th grade math word wall.

A teacher asked if I could also add references for finding GCF and LCM the traditional way to the 6th grade math word wall. I used the same numbers as the ladder method so that students could compare the two methods and decide which they like better.

**Activities for teaching GCF and LCM:**

GCF and LCM solve 'n check task cards |

Even in print form, these GCF & LCM solve 'n check task cards are self-checking. They also come digital in Google Forms (linked in the same file). Students answer both questions on a card then use the check number in the lower right corner to see if their answer is correct. Solve 'n check tasks can be given to students for practice in groups or individually or even used as an informal assessment. I used to like using task cards to assess students because they didn't cause students as much anxiety as quizzes. Lower student anxiety meant I could really see what they knew.

GCF, LCM and prime factors math pennant |

Students find greatest common factor, least common multiple and prime factorize in this GCF LCM math pennant activity that doubles as math classroom décor. Here I took a photo of the same pennant colored differently and where different methods were used to find GCF. Students can complete their pennants then decorate them with a little color. The end result makes for a nice classroom display of what students have learned.

GCF and LCM digital math escape room |

Here's puzzle #4 of a GCF and LCM digital math escape room. Students must unlock 5 locks by finding either the greatest common factor or the least common multiple of 20 number pairs. Questions are grouped 4 per puzzle, resulting in five 4-letter codes that will unlock all 5 locks. The entire self-checking escape room is housed in one Google Form with no outside links, making it a breeze to assign. If finding both LCM and GCF is too much for your students, there's also a GCF Only digital math escape room here.

There are more ideas for teaching GCF and LCM, including a video explaining the ladder method, in this GCF & LCM post.

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