The latest in education is that writing should be in every subject -- even math. So, if you are teaching writing in math, when will you teach math? Having a national curriculum doesn't take into account regional/state/local issues. For example, maybe an area has many families whose parents are engineers (like working for NASA.) Obviously, the parents are going to want the kids to have a stronger math program than a national curriculum that makes everyone the same. On the other hand, rural or inner city kids whose parents have little to no education can't possibly expect their kids to be reading at the same level as a kid who was read to daily before kindergarten.