... performance on seven specific tasks -- reading speed, single-word identification, spelling, accuracy, real and non-word reading, and reading comprehension ... They found that on average, children exposed to high levels of nicotine in utero -- defined as the minimum amount in one pack of cigarettes per day -- scored 21 percent lower in these areas than classmates born to non-smoking mothers. The children were tested at age seven and again at age nine. [emphasis mine]
Researchers have found that children born to mothers who smoked more than one pack per day during pregnancy struggled on tests designed to measure how accurately a child reads aloud and comprehends what they read.