It can be frustrating for both teachers and parents to work with children who have learning disabilities. You will have been in these situations where they will know a certain topic one day and completely have forgotten most all about it the next day.
It enrages parents who are not prepared for this phenomenon, but really it is quite common and a feature of the learning disabilities. This is how their brain functions. They do not do well with memorization of algorithms for math, but need thorough context and meaning before the topic will have sufficient connections in their brain to be able to be recalled at a time when they need it.
You could compare it like this. Imagine you are hanging a stone on a rope, tie it neatly with a bow and then go home for the day. The next morning, there is no stone and you’ll be lucky to find the rope back. Many things have happened that made the stone go its own way. The wind blew, the rain came, some birds sat on it, kids took a whack at it, etc.
So now you connect the stone with a rope, a wooden basket, some duct tape, glue and a leather band, and now the stone has enough connections to be there when you want it.
Likewise with the outcome of 6+4=10. This is bound to get lost by all the other distractions and adventures in the child’s brain. So if you not only show 6+4=10 but also 4+6=10 and 4 is two time 2 and 6 is two times 3 and 10 is two times 5 and 2+3=5 which is half of 10…. Now we are on our way to get some more meaning around the numbers and we make progress. Slowly because you’ll soon find out that you’ll need regular “spiral review” to circle back to topics to ensure all the connections are still there, like you’ll have to check on the stone from time to time to see if that duct tape holds.