Robert was small and slightly underweight at birth. He had been exposed to drugs while his mother was pregnant. His cries sometimes sounded high-pitched, and he was often tense and rigid. Robert's mother moved twice before he was two years old. First she moved in with her mother; then she moved out again. Robert was not quite as quick as other children at learning new words. He was not good at sorting blocks and learning to pick up beads. Robert had a new sister, a half-sister, when he was three. There were not many books or magazines at home. When Robert began kindergarten, he had trouble learning the letters. Sometimes, he seemed a little tuned out and apathetic.

Neighborhood poverty and family disorganization contributed to Robert's delayed developmental course – as did the prenatal insult of Robert's mother's substance abuse. In our society, prenatal drug exposure is a major public health problem. Many drugs used during pregnancy travel freely through the umbilical cord and cross the fetal blood–brain barrier. What kind of effect would such drugs have on Robert's development? A developmental systems model suggests that the interplay of many factors influenced Robert's development. The impact of drugs on the fetus during the pregnancy depends on the timing of use, dosage, level of prenatal nutrition, and individual differences among mothers, some of which may be heritable. The impact of maternal drug abuse on subsequent child development is even more complex and multidetermined.