In a study to see if computer-assisted instruction helps children with reading, difficulties learn reading skills at a faster than normal rate, an educational psychologist arranged for a child with reading difficulties to have access to a set of computer learning programs instead of the normal reading curriculum for one term. At the end of the term, he tested the child on a standardized reading ability test. What potential confounding variables must be balanced in this research? Explain what balancing procedure would be best for this experiment.