Ladder Method for GCF or LCM

So, even though it’s been around for a while, I’m suddenly noticing the Ladder Method popping up all over Pinterest and several Math sites.

My question is why?  Ladder Method

How is this helpful?  Yes, students can get the right answer, if they perform all of the steps correctly and remember which numbers to include for their LCM solution and which numbers to include for their GCF solution.

But I don’t think it teaches them anything conceptually, and I recommend staying away from this approach.

Students end up multiplying to find their final answers with both the GCF and the LCM version of the Ladder Method.  But we want students to understand that finding the GCF is all about dividing.  In a real-life GCF situations, division should be the focus.  With the Ladder Method, students just mutliply the left half of a giant L, with no idea why they are doing so.

And when students find a least common multiple, the whole point is to focus on the multiples that a pair of numbers share.  This Ladder Method focuses on multiplying factors, and students don’t need to demonstrate any knowledge of multiples at all.

I literally have my students cross this section out of their consumable Math textbooks.  Have you used this method with success?  Perhaps with advanced students who definitely understand the core concepts, and who are looking for a shortcut to be used with very large numbers, this would be a neat trick to show them.  But the Common Core standards do not require students in 6th grade to find the LCM of numbers beyond 12 or the GCF of number greater than 100, so I wouldn’t touch it with a 10-foot pole.


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