What, exactly, are they trying to teach with common core math, and is it necessary?

I’m finding myself in a unique position of trying to figure out what exactly the lessons want from the students, while simultaneously trying to teach it. By the time I figure it out, we’re on to a different subject.
I can see the concept…finding answers to math problems in different ways. It’s also getting a jump on Algebra, and I guess it’s fine, but is it really necessary? The kids who got it the other way get this new way just fine. The kids who didn’t get it the other way still don’t get it this way, and it makes it very difficult for parents to help with homework to boot.

What are your thoughts on it?