I do get the idea of teaching children different strategies for maths. I don’t think having more than one way of working things out, especially for mental maths does any harm. I can also see that some children might do better for different strategies than others.
The thing is that by the end of Year 5 they have to know the old-fashioned way that all the parents were taught at school. I know in my son’s case it would have meant a lot less stress if we had gone straight to that. How he hated number lines. So did I to be truthful. They seemed pointless and he hated having to draw all the lines. Doing sums with a number line took 3 or 4 times as long as other ways. Often he’d already done the sums in his head before he picked up the pencil. It was just silly. Maybe some children like them, but I remain to be convinced.
The grid method is one I personally loathe. I spent an hour of my life on YouTube trying to work out a way of using it with decimals. I don’t know if you can. I still don’t. Everyone doing their nice little YouTube tutorials picked nice easy sums. We didn’t have any problems doing the easy ones, we wanted help with the difficult ones. It wasn’t there. I gave up and taught my son long multiplication. It worked.
That’s the thing. It works. Once you have learnt it, you will have that skill for life. It works every time and can cope with whatever you throw at it. And in any case they’ll use a calculator for the really complex stuff. Why not just teach long multiplication and if some kids don’t get it you can teach them something different? Then they’ll be able to do long multiplication in Year 3 or 4 rather than Year 5 and can move onto something else.