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 .