Everyone knows what it is to be hungry. Or do they? Most of us, most of the time, sate that basic need so quickly that it never affects our ability to get through the day.
Teachers across Scotland, however, have been telling TESS for some time that pupils are arriving at school hungry. With each passing month, they are encountering more and more children who cannot function because they are not eating properly - and sometimes, for long periods, not eating at all.
Last month, the EIS teaching union decided to take action, with a flurry of collections for food banks and letter-writing campaigns to highlight how hunger is affecting children's ability to learn. Meanwhile, a motion was put to the union's national council asking for research and advice for its 55,000 members on what to do if a pupil has not eaten.
This assessment of the depth of the problem is no trade union hyperbole, according to Dr John McKendrick, a poverty expert at Glasgow Caledonian University.
"We are at a turning point," he says. "After a decade or so when we became accustomed to reductions in the level of child poverty in Scotland, we are now witnessing increases - significant increases. All the available evidence points toward significant rises in the number of children who will be experiencing poverty in Scotland. It is bleak and it will get much bleaker before it gets better."
Evidence of the ramifications for children's nutrition is starting to mount up. A recent report by children's commissioner Tam Baillie and charity Save the Children (bit.lyPovertyEduSurvey) asked pupils around Scotland for their views on poverty and education. Time and again, food - or the lack of it - was mentioned.
"Aye, if you don't eat then you've not got the energy and then you can't think," one pupil said.
Often, bad behaviour masks the real issue. At a national poverty conference organised by the EIS, former Barnardo's chief executive Anne Marie Carrie spoke of a boy who, after getting into trouble for not having his PE kit, exploded and swore at his teacher. It emerged that his alcoholic father had eaten the boy's dinner the night before - a tin of tomato soup, the only food in the cupboard.
The effects of hunger are often more insidious, however. Secondary teacher and TESS columnist John Greenlees recalls working in an area where 91 per cent of pupils were eligible for free meals.
"The first thing you noticed was how small some of the students were," he says. "The combination of malnutrition and ill-health left many of the severely disadvantaged children underweight, pale and lethargic."
Widely quoted US research (bit.lyHungerResearch) lays bare the impact of hunger on children's schooling: they are "significantly more likely" than other students to be in special education, to repeat a grade and to receive mental health counselling. Hungry children showed up to 12 times as many symptoms of "conduct disorder", such as fighting, blaming others for problems, having trouble with teachers, stealing and not listening to rules.
There has been a "huge rise" in pupils arriving at school without having eaten, says Susan Quinn, education convener of the EIS teaching union and secretary of the union's Glasgow branch, who launched last month's motion.
Quinn, a primary headteacher, recalls one P1 girl whose mother had reassured her that, although there was no breakfast, the school would give her food at lunchtime. "It may not be just that they've not had breakfast, they've maybe not had anything hot since lunchtime the previous day," she says.
When the union asked members last year how poverty was affecting pupils, tales came in of hungry children stealing food from classmates, pupils looking ashen day after day and of more families seeking referrals to food banks.
"To me, it's worse than it's been, it's more prevalent," Quinn says, adding that teachers in seemingly more affluent areas are, perhaps for the first time, starting to see signs of children going hungry.
Meanwhile, local authorities have been quietly chipping away at budgets designed to offset hunger. As far back as 2012, TESS revealed that a third of councils had already stopped offering free fruit to pupils and more have since followed suit. Now, Quinn says, many teachers keep an emergency stash of fruit in their drawer.
"I'm very angry that we continue in this day and age to have children coming to school without proper food," Quinn says. "I'm angry that we seem to have accepted that food banks are something that's going to exist in society."
A report released by the Joseph Rowntree Foundation last year (bit.lygapJRF) suggests a degree of complacency around efforts to tackle poverty in Scotland. Numerous recent initiatives have been designed to combat poverty's effects on education, but the study reveals that little evidence exists of whether or not they are actually doing any good.
Poverty and hunger have, however, become highly political issues, as the SNP and Labour tussle to prove who has the moral authority to rule in Scotland. During last year's independence referendum campaign, poverty was as ubiquitous an issue as immigration is in Westminster politics.
The SNP made a great show of its P1-3 free school meals initiative, launched this month, although the impetus came from a similar Westminster policy instigated by the Liberal Democrats. Scottish Labour criticised the SNP policy - despite its widespread support from charities and trade unions - insisting that it benefited the rich more than the poor.
Poverty and hunger may be front and centre of Scottish politics, but food bank referrals are still soaring.
East Lothian's food bank started as a "very, very small operation" in December 2012, its manager Peter Dicker explains. But by November 2014 it was sending out almost triple the amount of parcels it had delivered in June 2013.
The food bank has fed 2,187 people since April (some people may have been counted more than once), of whom 782 were children. Often, it is schools that ensure children do not go hungry. Since April, the food bank has had referrals from 11 schools - East Lothian being a small authority of 20 primaries and six secondaries.
"The headteacher is at the front line seeing the problem," Dicker says.
Referrals come from almost every corner of the authority. Dicker says that people would be surprised at how well-spoken some beneficiaries of food banks are, and there are all sorts of reasons for their plight. One woman with no source of income and four children under 16 was bereft after her husband left and cleared out their bank account.
But the feeling of hunger is universal. It is "devastating" for any parent to send their child to school on an empty stomach, Dicker says.
"I was in the army for 22 years, I know the value of a good breakfast," he adds. "I know what it's like to be hungry, to be on exercise and have that gnawing feeling in your stomach. When you have nothing, you're grateful for anything."
`I ended up bringing in a loaf of bread': a secondary teacher's story
"Last term one girl was in tears in the corridor. Her friend took me to her. `You'll find she's not eaten all day,' she said. Lunch had just finished so I had to raid the staffroom and, with the permission of the various owners, provide her with some cereal and cereal bars to get her through the day.
"A few years back, a girl in my registration class had left home and was staying with her sister. She was in a mess and never ate. Her behaviour and attainment slumped. I ended up bringing in a toaster and a loaf of bread, and we all had toast in registration - that masked her need for it. That was in the days of councils owning schools. The public-private partnership environment now forbids toasters.
"I help out at the school breakfast club. We get between two and 10 kids coming - they don't eat at home for a variety of reasons. We could put money on a kid who failed to turn up for breakfast club ending up in real bother in classes later.
"Not all teachers understand the behaviour traits related to hunger and deprivation. I work closely with food banks and poverty campaigners. Some colleagues dismiss families who supposedly holiday in Spain every year and have Sky with a 50in flatscreen television. Such stereotyping disgusts me."