Check out this figure from a fairly technical report on task switching and cognitive flexibility. The interesting thing to see is how the left ventrolateral prefrontal cortex seemed to be important for switching gears with new conceptual tasks.
In fact (lower picture below), these areas take quite a lot of time to mature (blue in with the color code below) as seen from the Teen Brain figure below.
How often do we see young children who self-combust with task-switching activities in conventional classrooms? Sometimes this is due to a hopeless compromise between the different needs of short and long attention children. Some with very short attentions will not get any more information if they are asked to devote longer times on a task, while others may lot learn well if tasks are switched too frequently.
There is a biological basis that makes task switching difficult for young (and even older) children - and it gets better with age.
Conceptual and Response Flexibility and fMRI
Teen Brain and fMRI