Parents and teachers recognize them - the kids fuming or fretting over switching tasks, or others are left behind with every change in activity. Problems with task switching are often lumped into the category of Executive Function (as in prefrontal, the simplistic ADD / ADHD idea), but it looks like the truth is more complicated than a simple answer.
In fact, it looks like a complicated and coordinated network of brain areas (ACC/pre-SMA, insula/operculum, posterior cingulate, precuneus, parietal cortex) required for efficient task switching - and that may explain why it doesn't take much to disrupt the system. It's certainly not just prefrontal.
The authors also discuss their work in the context of a previous study's findings-better task switching was seen with stronger pre-SMA activity before performance of the task, whereas high pre-SMA activity during tasks was associated with increased work and poorer switching ability.
If this is true, it gives credence to the practice of the "10- or 5-minute warning" for kids. It's probably more efficient to prime the pump with consistent and gradually tapered warnings over time, rather than expect that repeated exposures to task switching will improve cognitive control.
By the way, if you haven't seen the news articles about Tourette's syndrome and cognitive control, check them out. Unfortunately articles are not yet free. Researchers found that Tourette's kids were better at an eye movement cognitive control task than unaffected controls, presumably from having to practice all the time due to their condition.
Task Switching and fMRI
Increased Cognitive Control In Tourette's
Eide Neurolearning Blog: Task-Switching, Emotional Motivation, and Reward