There's an upper bound to how efficiently say elementary school kids can learn unsupervised, and if you discard the outliers it's not very impressive. School teachers are not just doing busywork sent down by bureaucrats; much of it is still teaching in the class, checking student's progress, grading the homework and so on.
As to the working in bursts I used to think of it as a manifestation of creativity and talent in heroic stunts. Years later I see it differently: if you do one hour of actual work in a week, you are procrastinating/slacking for the other 39 hours. Even, predictable pace of work is a hallmark of professionalism. At least now I try hard to keep my progress steady and predictable.
