"What I often hear, at the family math academic support sessions I offer, is "I can't help my son or daughter with math."
I am a big advocate for parents helping their children with math (and the other subjects as well). Now in the third year of working with my son (he is in third grade), here is the reality I have realized. It is virtually impossible for parents to help their children with math, at least not with the new elementary curriculums.
So much of the curriculum is filled with activities that are simply mathematically beyond the student's maturity that "helping with math" becomes nothing more than helping them follow instructions. For example, a recent activity relating to mental math was to perform subtraction of two numbers by rounding the second number to an "easier" number, performing the subtraction and then adding or subtracting the difference from rounding. If we had 153 minus 47 then we could do this as 153 minus 50, which is 103, and then add 3 to get 106, the final answer. This is certainly a valid technique, as is completing the square, but if the kids are not yet mature enough to understand its significance they will not own this after all is said and done.
Instead of a steady progression of getting better and better with numbers, the curriculum jumps from one technique to another. Techniques which I am sure pleased the adult authors but which I am also sure do not have the intended effect on third graders. And it isn't just about "technique", even borrowing and carrying is a technique, but if every week is a new technique then the result isn't the understanding of addition or subtraction it is how to follow instructions. Math is not about following instructions. In fact, nothing academic is about following instructions.
Thus, the parent isn't able to help teach math because the students aren't learning math, they are learning about techniques, a very shallow learning at that. It isn't like the student comes home and says "Mom, we are learning addition." and the mom can start teaching them about addition. It isn't even a case where the student can come home and say "We are learning X" because they are not learning anything much at all unless you consider things like how to make a fart sound with your armpit learning. What happens is that the student comes home each week with a worksheet that exemplifies some process and the "learning" becomes the parent simply trying (with their child) to follow the instructions. Even if the parent understood "what" was happening mathematically (and most wouldn't), there is little chance to explain that in the time allotted to an 8 year old kid.
In the end I am pleased with my son's progress (not due to the school unfortunately). The examples like the subtraction problem above, he can do in his head because he has optimized the carry operation and does it without actually carrying, but when we do it as it is taught, he is just following instructions. I will back fill later.