Homework With a Phone Beside It Is Not Multitasking. It Is Switching, and Switching Costs
Nobody does two thinking tasks at once. The mind switches between them, every switch costs time, and practice with screens does not make it free.
People do not multitask on two tasks that both need thought. They switch between them, and decades of task-switching research show every switch costs time, with bigger costs for more complex tasks and some cost left over even when the switch is expected. Heavy media multitaskers are not better at it; in the original 2009 study they did worse on a switching test, though later research is mixed.
Watch a teenager do homework with a phone on the desk and it looks like two things are happening at once. A maths problem is being solved and a group chat is being answered.
That is not what is happening. What is happening is one task, then the other, then the first again, many times a minute. Each of those changes has a price.
Try the cost of interference yourself
The oldest demonstration of attention getting in its own way is from 1935. J. R. Stroop asked people to name the ink colour of printed words. When the word itself named a different colour, such as RED printed in blue, naming the ink was slower than when the two matched.
Reading is so practised that it runs whether you want it to or not, and it has to be overridden. That override takes time.
Stroop is not multitasking. It shows the basic fact the rest of this article builds on: a mind cannot fully ignore one thing while doing another.
What switching between tasks costs
Task-switching experiments ask people to alternate between two simple jobs. One example is judging whether a number is odd or even, then judging whether it is bigger than five. The result is one of the most reliable in cognitive psychology.
Responses are slower, and often less accurate, on a trial where the task changes than on a trial where it repeats. This is the switch cost.
Three findings matter for homework:
1. The cost grows with the complexity of the tasks. In a 2001 series of experiments, Joshua Rubinstein, David Meyer and Jeffrey Evans found switching costs were larger when the rules of the tasks were more complex. A maths problem and a message thread are far more complex than odd-or-even.
2. Preparation shrinks the cost but does not remove it. In a 2003 review, Stephen Monsell described how knowing that a switch is coming, and having time to get ready, reduces the cost. But a residual cost usually remains even with generous preparation time.
3. The cost is paid on every switch. A student who checks a phone twenty times in an hour pays it twenty times, plus the time spent on the phone itself.
The last point is the one that turns a small laboratory effect into a large real one. A fraction of a second per switch sounds like nothing. But the laboratory cost is measured on simple, well-rehearsed rules. Getting back into the middle of a half-solved equation is very likely a much bigger reconstruction.
"But they grew up doing it"
The obvious objection is that Generation Alpha has always had several screens. Surely a lifetime of practice makes them better at it.
The best-known test of that idea found the opposite. In 2009, Eyal Ophir, Clifford Nass and Anthony Wagner compared heavy and light media multitaskers. The heavy multitaskers were more easily distracted by irrelevant things around them and in memory. They also did worse on a test of task-switching ability. The authors put this down to a weaker ability to filter out the task they were not doing.
That was a single study of adults, and it attracted a lot of follow-up. In 2018, Melina Uncapher and Wagner reviewed what had accumulated. The literature is still sparse and the findings are mixed. On balance, heavier media multitaskers tended to perform worse in several areas, especially tasks that depend on sustained attention. But many studies found no difference. And nobody has shown which way causation runs: multitasking might weaken attention, or people with weaker attention might multitask more.
So the evidence runs from "worse" to "no difference", and the review gives no support to the idea that heavy multitaskers come out ahead. The educational researchers Paul Kirschner and Pedro De Bruyckere put the conclusion bluntly in the title of a 2017 paper, which calls both the digital native and the multitasker myths.
Our article on what "digital native" gets wrong covers the first half of that claim.
A phone that is not being used still competes
Switching is not only about picking the phone up. Every glance at a lock screen, and every buzz that has to be ignored, asks for a small decision about whether to switch. That decision is itself a small task.
This is why "just don't check it" asks a lot. The student is not doing homework plus nothing. They are doing homework plus a continuous job of not switching, which is roughly the Stroop problem stretched over an evening. Our article on attention in a short-form world covers the related idea of attention residue.
What actually reduces the cost
These follow directly from the research. They are sensible applications of it, not tested homework programmes.
1. Remove the switch, not the willpower. A phone in another room removes the decisions as well as the switches. Face down on the desk removes neither.
2. Batch the messages. Twenty-five minutes of work, then five minutes of replies, means a handful of switches instead of dozens. Preparation reduces the cost, and a planned switch is a prepared one.
3. Leave a note before switching. A single line such as "next: multiply out the bracket" shortens the reconstruction when you come back. It turns an unprepared switch into a partly prepared one.
4. Put the hardest task where there are no switches. Complex tasks carry the biggest switching costs, so they gain the most from an uninterrupted block.
5. Do not treat "I can do both" as a skill to trust. The cost is paid as a slower pace, not as a moment anyone notices, which makes it easy to underestimate.
If homework is also being put off entirely, that is a different mechanism with a different fix. See why children put off homework.
The honest summary
Switch costs are among the most replicated findings in attention research. They grow with task complexity, and preparation reduces them but does not remove them. The idea that heavy media users are better at multitasking has no support. The original evidence pointed the other way, and later research ranges from worse performance to no difference.
The exact cost in minutes of a real evening's homework has not been pinned down, and any single figure you see for it is an estimate. The direction, though, is not in doubt.
Sources
- Stroop, J. R. (1935). Studies of interference in serial verbal reactions. Journal of Experimental Psychology, 18(6), 643–662. doi.org/10.1037/h0054651
- Rubinstein, J. S., Meyer, D. E., & Evans, J. E. (2001). Executive control of cognitive processes in task switching. Journal of Experimental Psychology: Human Perception and Performance, 27(4), 763–797. doi.org/10.1037/0096-1523.27.4.763
- Monsell, S. (2003). Task switching. Trends in Cognitive Sciences, 7(3), 134–140. doi.org/10.1016/S1364-6613(03)00028-7
- Ophir, E., Nass, C., & Wagner, A. D. (2009). Cognitive control in media multitaskers. Proceedings of the National Academy of Sciences, 106(37), 15583–15587. doi.org/10.1073/pnas.0903620106
- Uncapher, M. R., & Wagner, A. D. (2018). Minds and brains of media multitaskers: Current findings and future directions. Proceedings of the National Academy of Sciences, 115(40), 9889–9896. doi.org/10.1073/pnas.1611612115
- Kirschner, P. A., & De Bruyckere, P. (2017). The myths of the digital native and the multitasker. Teaching and Teacher Education, 67, 135–142. doi.org/10.1016/j.tate.2017.06.001