Imagine you were taking the SAT and every 5 minutes, somebody interrupted you and asked you a question like,
"Excuse me, do you know what time it is"?
"How do I get to the closest deli from here?"
"Want to hear a funny story about my most embarrassing moment? Well, here it is."
Every five minutes, for the entire 3 and 1/2 hours. What a disaster.
Wouldn't it completely disrupt your concentration? Could you possibly be expected to focus and do well while wading through critical reading passages and trying to figure out math questions about two trains leaving two different destinations, one traveling at 1/3 the speed of the other train?
No matter what score you got, you'd know you could have done better if that idiot would have just shut up and let you concentrate. You'd feel like you didn't even get a fair chance to do well on the test.
If you're answering emails, texting or checking Facebook every five minutes while you're trying to study, isn't that pretty much the same thing?