Just a thought... with the 7-8 year olds I have in maths club, I constantly ask them HOW they solve problems. Not "showing their work" per se, but when faced with even something simple like 9+5, what is it that they see in their minds? How do they arrive at the problem? Did they see 10+4? Did they imagine a timeline in their head and jump forward 5 places? I use visual spatial strategies (picture tree x tree is a washing line line for 3 x 3 = 9) to see if this resonates. So I try and work out what happens in their mind first. Two things happen: often their own explanation of how they got to an answer surprises themselves (!) And secondly, they're often really surprised by just how many different strategies that kids employ to get to the same answer.
So this is my long way of saying... ask your DS! jojo
