According to Roenneberg, age also has a big influence on chronotype. Toddlers tend to be larks, which is why they drive their parents crazy by getting up at sunrise. Teen-agers are owls, which is why high schools are filled with students who look (and act) like zombies. Roenneberg advocates scheduling high-school classes to begin later in the day, and he cites studies showing that schools that delay the start of first period see performance, motivation, and attendance all increase. (A school district in Minnesota that switched to a later schedule found that the average S.A.T. scores for the top ten per cent of the class rose by more than two hundred points, a result that the head of the College Board called “truly flabbergasting.”) But, Roenneberg notes, teachers and school administrators generally resist the change, preferring to believe that the problem is insoluble.