I'm doing some work that's having me look at the math common core and I'm curious about primes, composites and prime factorization. I teach 5th grade and one of our topics is primes and composites. Seems to me this is no longer part of 5th grade math under the common core. In 4th grade there's a standard to "develop and/or apply number theory concepts to find factors and multiples" (CC24A2). But I can't tell from this standard if that means in 4th grade they're then expected to do prime factorization, or if it's just listing factors and multiples. Is it also finding the GCF and LCM? And does this mean it's all happening in 4th and not touched on in 5th? I'm in PA but from what I understand our PA common core is based off the national common core. In my school we're switching math books this coming year and will be doing the common core this coming year for the first time. I'm planning out Khan Academy topics to cover per grade and basically am looking for insight on whether to include prime and composites at all, and if so, if 4th grade is the only grade to do it. Am also wondering whether to include GCF/LCM for 4th grade as well. Thanks to anyone who can help .

When I worked with our regional committee to write our curriculum based on CCSS, we included some additional expectations that we felt were necessary for student success with the overarching standards...could it be that's the situation with prime, composite numbers in your situation?

Quite possibly Cza. I think I'll just wait and see when I get our new textbook (Go Math) and see how they cover it in grades 4 and 5. But in the meanwhile, some insight from those already following the common core is great. What I do know is our fifth graders had a really hard time with prime factorization (which took me by surprise as I didn't think making factor trees and then the follow up prime factorization would be that hard) so I sincerely hope our 4th graders won't need to do it.

Here's the thing, we're all implementing CCSS now, but the narrow but deep focus called for by the new standards are just that: new....so we all have kids coming up who have had the 'soup to nuts' math curriculum we've been teaching for years, but not necessarily the deep understanding and fluency with what is needed to be immediately successful with common core....I know I'll have third graders coming up who haven't mastered their 'basic' facts in addition and subtraction, but my year is scheduled to start with multiplication...we're all going to have to do some supplemental 'catch up', skill and drill kind of stuff until the incoming students have a year or two of CCSS under their belts.

The terms students should learn to use with increasing precision with this cluster are: multiplication/multiply, division/divide, factor pairs, factor, multiple, prime, composite 4.OA.4 Find all factor pairs for a whole number in the range 1–100. Recognize that a whole number is a multiple of each of its factors. Determine whether a given whole number in the range 1–100 is a multiple of a given one-digit number. Determine whether a given whole number in the range 1–100 is prime or composite. This standard requires students to demonstrate understanding of factors and multiples of whole numbers. This standard also refers to prime and composite numbers. Prime numbers have exactly two factors, the number one and their own number. For example, the number 17 has the factors of 1 and 17. Composite numbers have more than two factors. For example, 8 has the factors 1, 2, 4, and 8. A common misconception is that the number 1 is prime, when in fact; it is neither prime nor composite. Another common misconception is that all prime numbers are odd numbers. This is not true, since the number 2 has only 2 factors, 1 and 2, and is also an even number. Prime vs. Composite: A prime number is a number greater than 1 that has only 2 factors, 1 and itself. Composite numbers have more than 2 factors. Students investigate whether numbers are prime or composite by • building rectangles (arrays) with the given area and finding which numbers have more than two rectangles (e.g. 7 can be made into only 2 rectangles, 1 x 7 and 7 x 1, therefore it is a prime number) • finding factors of the number Students should understand the process of finding factor pairs so they can do this for any number 1 - 100, Example: Factor pairs for 96: 1 and 96, 2 and 48, 3 and 32, 4 and 24, 6 and 16, 8 and 12. Multiples can be thought of as the result of skip counting by each of the factors. When skip counting, students should be able to identify the number of factors counted e.g., 5, 10, 15, 20 (there are 4 fives in 20). Example: Factors of 24: 1, 2, 3, 4, 6, 8,12, 24 Multiples: 1, 2, 3, 4, 5…24 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24 3, 6, 9, 12, 15, 18, 21, 24 4, 8, 12, 16, 20, 24 8, 16, 24 12, 24 24 To determine if a number between1-100 is a multiple of a given one-digit number, some helpful hints include the following: • all even numbers are multiples of 2 • all even numbers that can be halved twice (with a whole number result) are multiples of 4 • all numbers ending in 0 or 5 are multiples of 5

Thanks Rain, the PA document I have with the standards doesn't list it with that wording but it then does make sense that it's included in the 4th grade standard. Will make a note of it, thanks!

We've been told (and my own reading has confirmed, that there are a number of skills, especially in math, that are "understood." For instance, there is no mention at all of money in the first grade curriculum, yet they are expected to be able to count change when they enter 2nd.

I teach 5th and used the CCSS last year. We did not teach prime and composite numbers in 5th grade, it was done in 4th. What you will find is that you will spend a lot of time teaching gap skills the first year you use CCSS because students will miss large chunks of material due to standards being moved around.

With the counting money, it sure would make sense to have a standard in K or 1st grade that states the student should be able to identify coins. I'm still grappling with the challenge of having third graders be fluent in both multiplication and division facts. Not saying it can't be done, but the vast majority of my 5th graders didn't have this skill. Maybe 20% of my students were fact fluent in addition, subtraction, multiplication and division. And I had the second highest math group based on their 4th grade PSSA scores.

Thanks agdamity, that's what I'm thinking too - that the first few years of it will be hard as we fill the gaps.