Eliminating Careless Error is a remarkable book which shows children how to be SURE their answers in Arithmetic are correct.
Careless Error is the number one cause of failure in early mathematics (and even later on). It isn't that children don't know how to add, subtract, multiply and divide, it is whether they have the right answer or not which begins to define their inner view of themselves as mathematically proficient or not.
Eliminating Careless Error does exactly what the title says, 'It eliminates careless error'. This material SHOULD be taught in schools, but sadly is not. If they did teach it in schools, It would be possible that 'all children would get As in math'. The thought apparently horrifies school boards.