The New New Maths

I have been trying to help my eldest with maths, but predictably, I don't do it the right way. We spent a good while discussing the way she has been told to do it at school, but as she doesn't fully understand it and I can't work out what on earth she is doing it ended in frustration all around.

After much searching on the internet (you think that how schools are teaching subtraction would be a feature of at least one government website and that this would be easy to find - but no) I think I have kind of figured out what she has been taught to do.

It goes a bit like this...

Say you want to subtract 129 from 241:

241 - 129 = ?

What she does is round the 29 up to the nearest 10:

241 - 130 = 111

And then add on the one that we used to round up to 30.

241 - 129 = 111 + 1 = 112

This seems really weird to me and a possible cause of confusion. I suppose it makes sense as a strategy for mental arithmetic but as a formal method for substraction it's odd. I suppose that the idea is to give the student confidence in substraction and explain how things work later.

I suppose all parents are cursed with the inability to do maths the way they do it at school due to changing fads in educational practice. Does it have to be this way?