The difficulties children have when learning to read vary from child to child and from age to age. Some learning variables transfer as a child develops so that skills acquired in early learning stages transfer to more mature stages of development. However, the abilities that transfer and produce effects at one stage of learning may be different from those that transfer at later stages of learning. Among poor readers, at least two factors may differentiate among individuals: slow maturation of the brain and impaired cerebral function due to damage. Other complexities may also be involved in a child having difficulty learning to read so that it is inaccurate to suppose that poor readers form a homogeneous group. (TJ)