There's some extra context. In Khan's book "The One World Schoolhouse", he mentions some children who are branded "slow" under many traditional curricula. But a

There's some extra context. In Khan's book "The One World Schoolhouse", he mentions some children who are branded "slow" under many traditional curricula. But at some later point, they lurch forward, ahead of the rest of the class. (As if they had some confusion which caused them to think more deeply; then emerged with a deeper understanding.)