I don't know if she can't hold the numbers in her head long enough to manipulate them, or if it's something else. She doesn't have a "number sense" it's not fluidly understood that subtracting is the same as adding a negative or that, like in the example above, an even number plus or minus an even number isn't going to be an odd number". I know she was taught these things. I don't know why she doesn't "have" them.
Can this be an ADD thing? memory? lack of interest?
My daughter has very low (relative) working memory scores. Math is one of her biggest struggles and for the same reason you mention. She has a very difficult time keeping the numbers in her head while manipulating them. She also has ADHD and HATES math, so a lack of interest in the subject matter could be part of it. She can do the work but often/always makes mistakes in basic computing. It frustrates her immensely and she has trouble getting past the easy calculations to the rest of the work because she wants to walk away as soon as she makes a mistake.
I'm interested to see what others suggest to help. Right now, I spend the majority of time calming her down and talking her through problems to help her keep track of where she is. That might be okay in elementary school, but she needs some tips to help her work independently.
