Why would they change Maths?!
This is what we find a lot of parents saying. They would love to help their children but maths has changed. Actually maths obviously hasn't changed but the methods children are taught are often very different from the the way that many people (including myself were taught).
The reason for the change is actually to try to support children to understand why they are doing what they are doing. Back when I and many parents were taught maths we were given methods to learn and no one really cared if we knew why we were doing what we were doing.
Child: Why am I doing this?
Teacher: Because it works.
The thing is that if you know why you are doing something then you are much more likely to remember it and be able to adapt it to another situation.
Here is a really simple example of what I mean. I'm going to guess that when many people were taught how to do a subtraction such as 56 - 17 they were told 'you can't do 6 - 7 so you have to borrow one from next door' or something similar. 'Borrow one from next door' doesn't support any understanding of what is actually going on. Have a look at this youtube clip it really explains what you are doing when you are 'borrowing one from next door'.