The reading skills of American high school seniors are the worst they have been in three decades, according to new federal testing data, a worrying sign for teenagers as they face an uncertain job market and information landscape challenged by A.I. In math, 12th graders had the lowest performance since 2005. The results, from the National Assessment of Educational Progress, long regarded as the nation’s most reliable, gold-standard exam, showed that about a third of the 12th-graders who...