A-not-B error (also known as "stage 4 error" or "perseverative error") is a phenomenon uncovered by the work of Jean Piaget in his theory of cognitive development of children.
Perseverativt fel (eng. A-not-B error, stage 4 error, perseverative error) är ett fenomen som upptäcktes i Jean Piagets arbete om kognitiv utveckling hos barn.