An 11-years daughter of mine, when checking a piece of her writing or math exercise, where she has one or more errors, simply misses them, whispering contentedly something as 5*6=36.
Normally, if I ask her to count that multiplication, she does it correctly. She is GOOD in math, for example, and participates in math olympiads, not winning, but with good results. But if she already did a mistake, she starts to count the known example not as it should be, but as it is written already. The already written text becomes a new dogma. And the fact that I have checked the piece of text and gave her the number of errors in it, does not help. After the first pseudo-check, if she hasn't noticed an error, she becomes even more sure in correctness of the text and the second check goes even more formally. She repeats the check 1-2 times and after that refuses to do it and says she has it correct. If I prove it is not so, she agrees, but she still does not obtain any training in error finding.
What is interesting, if the erroneous exercise is complex, she recount it correctly. But if it is a simple, one- or two-step task, she can't.
I know, it is very difficult for absolute majority of people to see their errors. In writing, in mathematics - does not matter. As for me, I can find my own errors only by repeating checks, for I can easily do and later miss an error. But with effectiveness of my daughter she almost cannot find them at all.
Any exercises, methods, rituals, or god knows what else are welcomed.