When you are a parent, favouring one child over another is a recipe for family disharmony. So when a survey last autumn by the parenting group Netmums revealed that one in six mothers had a favourite child but would never admit to it, those who confessed to harbouring a soft spot for one sibling over another did so in hushed tones.

Favouritism in the classroom may not be quite so taboo but, rightly or wrongly, teachers often gravitate towards one pupil. “It’s a bit of an elephant in the room in teaching,” says Sue Cowley, an ex-secondary school teacher and author of Teaching Skills for Dummies. “Everyone has them, but no one likes to admit it.”

Just like favourites at home, the teacher’s pet is often allowed to get away with more than they should. For Francis Gilbert, head of English at a secondary school in greater London and author of I’m a Teacher, Get Me Out of Here, young Abdul was always the one.

“He could do no wrong in my eyes,” Mr Gilbert says. “He was so helpful and obliging.” So when a stink bomb went off in class, Mr Gilbert ignored the circumstantial evidence and punished an annoying and troublesome boy called Steve. Despite desperately proclaiming his innocence and enlisting the persuasive skills of his mother, Steve’s fate was sealed. The next day, Abdul confessed. “I was gutted,” admits Mr Gilbert. “Even then I wasn’t inclined to blame Abdul. Instead, I liked to think the other boy had bullied him into doing it.”

Such injustices may be widespread, according to the Equity Formation in Schools study, an international research project involving 25,000 teens. Almost 80 per cent of pupils from the UK felt that not all pupils were treated fairly by their teachers. They believed many had favourites. Teachers’ pets tended to be girls, or particularly bright, wealthy or conscientious pupils, the report found.

But it’s not always a conscious decision. Mr Gilbert does not knowingly base his favourites on gender or class. Instead, he is fond of those who are helpful or friendly, without being overly sycophantic. “The grovellers are just as irritating as the naughty children,” he adds. Another teacher admits to clicking with some pupils more than others, “often for reasons I can’t identify”.

But not all discrimination is bad, argues Professor Stephen Gorard, co- author of the 2008 report. Pupils expect and accept that a good attitude is rewarded, or that work is marked according to its worth. What they do not like is when recognition is carried into less deserving areas, such as the A-grade pupil who is solely exempt from cross-country running. “It is this type of discrimination that leads to greatest grievance,” says Professor Gorard. “Once teachers start appropriately favouring a pupil in one domain, it creeps across into other inappropriate domains.”

When pupils were asked what one thing they would change in schools, the largest proportion (38 per cent) said they would ensure that teachers reward or punish pupils more fairly. For instance, one contributor felt aggrieved when two similar misdemeanours were dealt with differently. “I forgot my PE kit and so did another girl in our class,” she told researchers. “The teacher fined me pound;2.50 and not the other girl, saying that it was the first time she forgot her kit.”

It’s easy to see how favouritism, or having least favourites, can become a vicious cycle. Those who feel marginalised will lack the incentive to work or behave, making them even less appealing in the eyes of their teacher.

“All the indicators show that a lack of respect fuels disaffection,” says Professor Gorard, “especially in the 14 to 19 category.” In his study, 31 per cent of pupils craved greater respect from teachers.

Paul Mawer, a chartered child psychologist in the West Midlands, often sees pupils who blame their lack of success on a teacher’s dislike of them. “They resent it strongly,” he says. “It rationalises and re-enforces their poor behaviour or attendance.”

Mr Mawer himself admits to having favourites when he taught in primaries in Birmingham during the Eighties - often rooting for the naughty ones. Ironically, the ones he least liked seemed to have the greatest affinity for him.

“The other pupils know for sure who is favoured, no matter how hard teachers try to hide it,” he adds. “Children are able to read things far better than we give them credit for.”

One of the more complicated scenarios is when a member of staff teaches their own child or relative. Well aware that they must hide any signs of favouritism, they can over-compensate and become overly strict with their offspring.

“It’s hard to get the balance right and treat them like the others,” admits one teacher whose young son is at her school in the Midlands. “You are so conscious of not wanting to favour them in any way that you go to the other extreme if you’re not careful.”

Another teacher remembers a quiz for the whole of Year 6, which included her daughter. “She didn’t answer a single question. She said later that she knew she couldn’t be seen getting a prize from me.”

Irena Barker, a reporter for The TES, was the headteacher’s daughter at a Peterborough comprehensive. Her father was careful not to exhibit any favouritism, but that did not stop other members of staff responding to her differently.

“Some gave me far too much attention. Others were deliberately standoffish, fearing I would discuss their badly-planned lessons with my dad. Which, to my shame, I did.” But, the experience was generally OK.

Mr Mawer would always caution against any partiality, whatever the circumstances. He does not believe favouritism benefits anyone, least of all the “chosen ones”, who may get spoilt, teased by their peers, or prove woefully ill-prepared when their next teacher fails to pay them the same attention. “Pupils like teachers who are firm and fair,” he argues.

Professor Gorard says that although teachers are entitled to have favourites, they must ensure consistency. “Young people feel the same universal sense of injustice as the rest of us. Pupils treated with respect and autonomy are more likely to trust others and be prepared for the more disadvantaged to be given extra help.”

Not all pupils are easy to respect, especially those who have steadily built up a bad reputation. At one school Inset course, almost every member of staff chose the same boy as their least favourite pupil. Despite his terrible reputation, it turned out that the boy had made a fantastic drum case in a design and technology lesson.

“It emerged that he was great to work with,” says Ms Cowley, who led the course, “so long as you found something that made him feel a sense of success.”

She admits that she had favourites - usually rebellious pupils who challenged the system - but she worked hard to hide her feelings. “You’ve got to fight the instinct, because the pupils can tell if you’re not fair and then they do react against it.”

Ms Cowley says a common trap teachers fall into is to ask the “nice” child to stop disrupting the lesson in a pleasant manner, while the “awful” pupil is shouted at for a similar misdemeanor.

The type of response can set the tone for future behaviour, but some teachers are unapologetic. “If children have the social skills to be friendly, amenable, or simply work bloody hard for you, they should be acknowledged,” says one primary school teacher. Another says that he is more comfortable having “favourites and less-than-favourites than having two or three in my class who I simply forget are there”.

Part of the problem is the widespread discrimination young people face in society. Teenagers in Professor Gorard’s research complained of being treated unfairly in shops, restaurants and most public places, especially when in a group.

Contributors also complained of violence, theft and bullying by their contemporaries, which left them feeling isolated and afraid. Where teachers were blamed was when they failed to deal with these high-level incidents effectively, maybe because their own prejudices got in the way.

It is essential, therefore, that rules are applied across the board, says Professor Gorard. “Trainee teachers need to formally consider when and where they discriminate, and the impact it will have on their pupils.”

When Ms Cowley taught at schools, she would consciously give troublemakers or less liked pupils added responsibilities. She gave one a major role in the school play. “Afterwards, he told me how great it was that someone had had faith in him,” she says. “He was really chuffed at the reactions to his performance.”

But one teacher’s favourite is another’s nemesis. Ms Cowley was on the cusp of naming her own child after her favourite pupil, until a friend and colleague dismissed the girl as intensely irritating.

Quiet, hard-working girls are most likely to be elevated, according to Mr Mawer, but he adds that other teachers prefer the “lovable rogues”.

He sees a lot of children in care become favourites because they are particularly good at relating to adults, especially in small groups. “It’s a skill they’ve had to learn,” he says. “They may have been charged with serious assault, but they can be extremely socially adept. You see the adults who work with them just melt.”

Who’s the fairest?

• Belgian teachers are least likely to have pets, according to 44 per cent of their pupils.
• Teachers in France are most likely to favour the clever pupils (56 per cent).
• Spanish teachers favour hard workers, say 78 per cent, but are more likely to punish some pupils more than others for similar offences.
• Italian teachers are the fairest at handing out punishments, say 63 per cent, and least likely to treat rich children better.
• UK teachers give pupils the fairest marks for work, say 82 per cent, but are most likely to favour girls over boys, according to 35 per cent.