Fourth and sixth grade children differing in reading proficiency read and commented on brief expository passages containing three different types of embedded problems (nonsense words, prior knowledge violations, and internal inconsistencies). Half of the children were specificially instructed as to the types of standards they should apply in order to detect the problems (lexical, external consistency, and internal consistency); the remaining children were simply instructed to look for problems. Both quantitative and qualitative differences in standard use were revealed by the children's comments about all parts of the passages. Older and better readers used more different standards and they used them more frequently than younger and poorer readers. The lexical standard was more likely to be adopted spontaneously than the other two standards and it was the only standard used by a substantial proportion of both younger and poorer readers. The results demonstrate that children differ in their ability to decide for themselves whether or not they understand but that their performance depends in part on the amount of guidance they are given. (Author)