Today's students have access to all kinds of gadgets and apps to aid their learning, but could these electronic devices be doing more harm than good?

A new study suggests the very presence of phones in a lecture hall can knock down grades overall.

The research found that when phone or laptops were allowed in a lecture hall, final exam performance dropped by as much as 5 percent on average, or half a grade – even for those students who didn't actually use a device.

It's a small study that needs further investigation. But the early results indicate that even just having gadgets on show in a lecture hall is distracting for the whole group, according to the researchers from Rutgers University in New Jersey.

"These findings should alert the many dedicated students and instructors that dividing attention is having an insidious effect that is impairing their exam performance and final grade," says one of the team, Arnold Glass.

"To help manage the use of devices in the classroom, teachers should explain to students the damaging effect of distractions on retention – not only for themselves, but for the whole class."

The study was carried out with the help of 118 psychology students during the course of a term. For half of a block of lessons, electronic devices like phones, laptops, and tablets were allowed; for the other half, they were prohibited.

There was even an invigilator on hand to make sure no one was sneaking a look at their mobile when they weren't allowed – though the students largely complied with the rules, the researchers report.

At the end of the block of lectures where devices were allowed, students were quizzed about whether they had used them for non-academic purposes.

Based on quick tests carried out during the lessons, having devices like phones and laptops didn't seem to affect short-term comprehension: the students showed no change in how much information they had taken in.

It was in the final end-of-term exams where there was a difference – the students' scores dropped an average of 5 percent in the exams that were based on material taught while gadgets were allowed in the lecture hall.

Based on a statistical analysis, that difference held whether or not the gadgets had actually been used for something other than learning.

Could a neighbour playing with his or her phone affect how much of a lecture you were able to remember? Based on this study, that could be the case.

According to the researchers, most students made use of electronic devices when they were allowed to, making it very hard for those who were trying to abstain from keeping their focus entirely on the content of the lecture.

The small number of people involved here, and the short-term nature of the study, means it's too early to make any broad conclusions about how the presence of gadgets impacts long-term learning, but there does seem to be something happening here.

It echoes research we reported on last year, showing that the very presence of a phone – even if it's turned off – can sometimes reduce mental capacity. Maybe these devices are much more distracting than we realise.

The team behind this study wants to see more research carried out in real classroom and lecture hall conditions to better understand how the added convenience of phones, laptops and tablets could be hurting academic performance overall.

"The finding that divided classroom attention ultimately reduces exam performance suggests a re-calculation of the risk/benefit ratio of technology that disables devices and applications not for educational engagement," conclude the researchers.

The research has been published in Educational Psychology.