One argument in this literature is that the "year-round" calendar
reduces summer learning loss. Consider the assumptions behind the contention
that reducing summer from 12 weeks to 6 weeks is going to have much of an
impact. It assumes that relatively little forgetting occurs between September
and June but a huge amount of forgetting takes place between July and September.
This seems implausible on the face of it. Moreover, the difficulties of
measuring such loss are often dismissed but they are large.