" The capacities that develop in the earliest years may be harder to measure on tests of kindergarten readiness than abilities like number and letter recognition, but they are precisely the skills, closely related to executive functions, that researchers have recently determined to be so valuable in kindergarten and beyond: the ability to focus on a single activity for an extended period, the ability to understand and follow directions, the ability to cope with disappointment and frustration, the ability to interact capably with other students. "

― Paul Tough , Helping Children Succeed: What Works and Why