All children must master the same elements of reading to become literate. The process of mastering each of these steps is simply more difficult for the challenged or 'at-risk' reader.
At-risk children are those who are likely to develop reading problems because of a family history of reading difficulties, their own early language problems, or low scores on a kindergarten-screening test. Reading performance tends to be stable, so by the time a child is in first grade, his reading ability already strongly predicts later reading achievement.
If significant progress is not noted within a few months, parents should seek further advice. There is always a reason for challenges. Children do not typically "out grow" or "catch up" on their own. Remember, reading is not natural to us; all children need to be explicitly taught.