"Recently the debate on screen time has come up quite strongly in education. Children are being exposed to too much screen time. Media headlines and limited research studies have been screaming about how our children are turning into addicts.  It is harming the development of their brain. It reminded me of the anti-Wifi or the intelligent design brigade which became popular a few years back or even way back in the 18th century when novels took off. 

Often all screen time is bunged up as one and people don't realise that the way we interact with a screen is of the utmost importance. Spending time video conferencing with a parent who is not in town or reading an ebook or an article is clearly not in the same category as time spent watching something inappropriate without supervision. The  quality of these different digital experiences has to be judged and weighted accordingly. Excessive passive screen time like TV viewing is indeed unhealthy however a child reading from a whiteboard or from a projection or on a device or a book is equivalent in value. 

Dr Michael Rich, the director of the Centre on Media and Child Health at Boston Children’s Hospital, says that he has seen cases of problematic interactive media use that keep children up at night. But, he adds, "I’ve also had kids who have been found staring wide-eyed and bloodshot at Harry Potter at two in the morning."

A longitudinal study published in the British Medical Journal of 11,000 British children in 2013 found that those who watched TV for 3 hours or more a day at age 5 had a small increase in behavioural problems two years later compared with those who watched for under an hour.
But it found no effects at all for those who played computer games.
adc.bmj.com/content/early/2013/02/21/archdischild-2011-301508.full

"Rosie Flewitt who studies Early Years and Primary Education at the Institute of Education (IOE) in London says touch screens are particularly motivating for children, allowing them to use a tool they can see is important to adults. “There is an unquestionable body of research showing that new technologies can engage children,” she says. Her own studies have shown that children who struggle to learn using books often made more progress with iPads."
https://www.newscientist.com/article/dn25297-children-benefit-from-the-right-sort-of-screen-time/

According to a literature review by the IOE commissioned by the Scottish Government "There is conclusive evidence that digital equipment, tools and resources can, where effectively used, raise the speed and depth of learning in science and mathematics for primary and secondary age learners."
http://dera.ioe.ac.uk/24843/1/00489224.pdf

Often studies citied like those in the https://www.psychologytoday.com/blog/mental-wealth/201402/gray-matters-too-much-screen-time-damages-the-brain which is used to highlight the dangers of screen time actually focus on Internet addiction studies which normally cover a limited number of participants. e.g. one study quoted (Hong 2013) had only 15 participants who were diagnosed with Internet addictions compared to 15 'healthy' ones.
http://behavioralandbrainfunctions.biomedcentral.com/articles/10.1186/1744-9081-9-11

Another one cited, Yuan 2013 only covered 18 participants 
http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0053055

Another one quoted covered 5 participants and compared them to 9 randomly selected participants
https://www.hindawi.com/journals/bmri/2012/854524/

Now compare this type of research to the beauty adverts we see on TV, they often use similar research models to justify their products - 195 out 200 using this product said that visible lines are reduced etc. Even they have more participants in their controlled studies. This does not make the above research invalid however the context and participants can't truly be representative of the wider population and we should use perspective to assess their validity. Also most of these focus on the brain’s reward centre which makes you feel good when you eat, use drugs or play video games normally using neurological images via fmri which perhaps isn't the most reliable technique in the first place. https://www.wired.com/2009/09/fmrisalmon/ 

Other experts like Dr Aric Sigman and Prof. Susan Greenfield, often quoted in newspaper articles “Social websites harm children’s brains” have been known to be selective about which research they share. Others have researched them in much more depth already.
http://www.badscience.net/2009/02/the-evidence-aric-sigman-ignored/

When Oxford University psychologist Dorothy Bishop analysed the research quoted by Prof. Greenfield she found a number of flaws. These are discussed here in depth.
http://deevybee.blogspot.in/2014/09/why-most-scientists-dont-take-susan.html

Even the BBC News article Extra screen time 'hits GCSE grades'  sensationalised the fact that the extra hour was after 4 hours of screen time a day. The research also pointed out that "pupils doing over four hours of reading or homework a day performed less well than their peers" It further points out that these children might have been struggling at school but does not make the same distinction for the one's affected by screen time. It also reports "All homework reported was classed as non-screen time and it is possible that screen-based homework was done which may have influenced our results." 

Another article from the BBC just published yesterday (13 Jan 2017) suggested that moderate screen use 'boosts teen wellbeing' http://www.bbc.com/news/technology-38611006

The American Academy of Paediatrics (AAP) have recently revised their guidelines on screen time in light of the overwhelming research evidence in favour of constructive use of technology.

"there is more evidence that they [preschoolers] have the ability to transfer knowledge from screens to the real world, including early literacy and math, and positive social and emotional skills and behaviors."

They now recommend 1 hour of screen time and prefer co-viewing for two year olds. The following article deciphers their policy document in an easy to understand way. Actual documents are linked in the further links section.
http://www.npr.org/sections/ed/2016/10/21/498550475/american-academy-of-pediatrics-lifts-no-screens-under-2-rule

For school going children
AAP does not suggest a limit as this depend upon each child's context. They do recommend co-viewing and supervision to avoid accidental exposure to sexual or violent media. Their research also quotes that anymore than 5 hours of passive screen time can lead to BMI increase over time. Which begs another question, how much time do children spend sitting? Perhaps that is more dangerous than screen time. What impact does this have for our classrooms? 

Dr Michael Rich says "Older children may need to use computers and/ or the internet to complete homework assignments. This kind of screen time shouldn’t be conflated with watching TV or YouTube videos." “What’s tough with guidelines is the press will only take certain things from it,” 
https://notes.childrenshospital.org/dissecting-aaps-new-guidelines-child-media-use-advice-mediatrician/

Dr Jenny Radesky from the University of Michigan finds that 

"Several health and developmental risks of excessive or inappropriate (eg, violent, adult oriented) media exposure continue to exist, primarily in areas of sleep, obesity, child development, executive functioning, and aggression."

But at the same time finds:

" Well-designed TV programs and interactive media can be educational starting in pre- school; but children younger than 2 years require adult interaction to learn from screen media.

http://www.sciencedirect.com/science/article/pii/S0031395516410291

A study from Stanford University in the US found that, by 18 months, toddlers from disadvantaged families are already several months behind their more advantaged peers on language proficiency. With the right content and context, digital devices can help bridge the divide.

One of the most extensive review of literature on this area was conducted by the London School of Economics (LSE) and goes beyond the media scaremongering. It recommends that parents should not automatically assume their child’s digital media use is problematic.

"Rather than limiting screen time according to an arbitrary figure, we recommend that parents consider screen context, content and connections by asking themselves:

• Is my child physically healthy and sleeping enough?
• Is my child connecting socially with family and friends (in any form)?
•  Is my child engaged with and achieving in school?
• Is my child pursuing interests and hobbies (in any form)?
• Is my child having fun and learning in their use of digital media?"

http://eprints.lse.ac.uk/66927/1/Policy%20Brief%2017-%20Families%20%20Screen%20Time.pdf

​I often find that people who don't fully believe in  technology are generally the first one's to jump up on these bandwagons. Often sourcing just one key video or research or a media report. Even educators are often reading research headlines and jumping on the bandwagon. Screens aren't going away and our children are going to be exposed more and more to them. How we manage that is our responsibility? We cannot blame a tool for how we choose to use it. 

School's often choose well designed activities to engage children with the learning material however if children at home are seeing parents distracted by their phones or are left unsupervised with passive screen time then perhaps greater awareness of best practice is the order of the day.
​
The argument for using less technology has long past. The use of technology effectively on the other hand has just started. As educators we cannot escape our responsibility to design well crafted and balanced learning experiences which allow children to engage with our curriculum content.

As Dr David Hill from the American Academy of Paediatrics says “Time spent in front of screens or devices isn’t inherently good or bad",  “Like everything else, it’s really about the content and how you engage with it”

Perhaps the debate has to move on from "screen time" to "screen purpose".