mental arithmetic

[Eveiebaby]

Just wondering what's the average age/school year a child should be able to do mental arithmetic at eg counting or subtracting from 20 without the use of a number square or number line etc...

Certainly they are starting it at y1. I don't know whether it is an expectation, though.

www.mumsnet.com/Talk/primary/1614756-mental-arithmetic
thought these two probably go together.

My ds can do addition/subtraction in his head consistently up to 20 and up to 100 with a few inconsistencies, but I am told this is very advanced for his age (reception). I would think yr 1 or 2 but maybe a teacher can confirm?

Thanks everyone for your replies and thanks for linking the other thread which I had not see LaBelle - it has some good tips!