A few years back I learned of a test that demonstrates the evils of multitasking. It's a way of training people not to say "no" but "not yet". I've shared it with many and will share it here as well...
Everybody knows how to count, the alphabet and Roman numerals. So, lay out the paper in three columns one entitled "Numbers", as second entitled "Alphabet" and the third entitled "Roman". Then instruct the group (that should include developers as well as managers) that they will be timed as they fill in the top 10 values for each column (1 - 10; A - J; I - X). The time trial will be run in two heats, the first time they should fill in the values by traversing the columns (1, A, I -- 2, B, II -- etc.). The second trial they will fill in the columns vertically. Compare the times between the two groups and discuss why they believe one was so completed so much more quickly.
The first trial is a very simple example of multmultitaskingle the second is the more focused sequential task. Explain that the more difidifficult task the more productivity that is being lost. To the greatest extent possible management should avoid situations where a great deal of context switching is required. If possible, make the context switch fall at a natural time (like after lunch or a meeting).
I hope you find this a useful example.