It's well after bedtime. But you can see the telltale light under the bedroom door. It's distinctive. It's the light from a computer screen.
What on earth is your little darling up to? Some addictive computer game, perhaps? You open the bedroom door ready to confront your offspring, ready to admonish - only to be told: "I'm doing my maths!"
The tale of "the secret mathematician" is true; and it's one that makes maths principal teacher Lynn Brown chuckle with delight.
And well should she chuckle, as the pupil in question was one of her S3 maths team at Craigroyston Community High in Edinburgh, who scored amazing success in World Maths Day 2010.
In the ages 14-18 category the team came top in Scotland, top in the UK and 32nd in the world.
"Well, we outstripped the likes of Harrow and Westminster schools, so it's not too bad," says Mrs Brown.
And if you consider there were 56,082 schools from 235 countries around the world taking part - and 1,133,246 pupils in all - the "14Craigies" (as the 14-year-old pupils called themselves) have certainly put their school on the map.
Each of the 29 students (with a roughly equal gender balance) had to complete 100 games at five different, and progressively more difficult, levels.
Each game lasted roughly one minute and the pupils played in "real time" against other pupils across the globe, their individual scores being added to the team score.
The race was to answer as many questions as possible within a minute, covering addition, subtraction, multiplication, division and equations.
"The pupils were in at 8am and stayed on till 6pm. Some continued from home on their own computers, while some came out of other lessons where they could to take part," says Mrs Brown.
The fact that the competition is computer-based and in "real time" was one attraction. But it was the competitive element that really got the pupils going.
"The whole `day' lasts some 48 hours and then we got a phone call from the organisers quite early on, saying we were fourth in the world. At that point, things really kicked in.
"But it wasn't just about competition. The team members effectively supported each other and that's what sustained them, what kept them focused," says Mrs Brown.
The success has obviously had a positive effect on the team members, boosting confidence and self-esteem. They were given a special assembly and at the school prize-giving they were given a standing ovation.
It has also added a "real buzz" to the maths department.
"I don't think the level of their achievement has really sunk in with the 14Craigies themselves, but it has given them a `can do' attitude. And if a pupil in any class now says `I don't have the answer' to any question, we can remind them that we are all now part of a school which tops the UK in maths."
Although delivered tongue-in-cheek, Mrs Brown's words do convey the sense of achievement and celebration that the whole school shares.
The maths department's main focus at the moment is on developing co- operative learning in keeping with the school's development plan.
"We're focused on active learning, co-operative learning, problem solving. That's been our primary focus within the department, putting that in place before we engage with other departments in the Curriculum for Excellence.
"Co-operative learning is an extra tool to use and the pupils are taking well to it, supporting each other while taking responsibility for their own learning, for both the academic and social goals in each lesson," says Mrs Brown.
Where both the co-operative approach and the competition success come together, she says, is in a growing sense of identity, of pupils believing in themselves more and having more faith in their abilities.
"It's also been good for community relations, and parents have taken a real pride in our success. I think because it's maths, parents think: `That's real! That counts!' You can enter teacher-and-parent teams too for World Maths Day. Maybe next year we will," she says.
Headteacher Margaret Russell believes the success has given "a real boost" to the maths department and to the pupils' sense of achievement. She confesses that she had no idea how well the school would do and - with a mastery of understatement - she adds: "Yes, you could say our maths is an improving picture ."
Courtney Dott, S2, member of the `14Craigies':
"We all worked really hard and we did it for the school. I know I did. I was hoping from the start that we would be the best in the UK. I really believed we could do it - and we did.
"I was a wee bit competitive at the start. Then I got more so. Then I got really competitive.
"It was great playing people from other countries, from Japan, Malaysia, Australia, the USA. I enjoyed the tension, getting the answers quick before anyone else.
"It was all about speed, the tension and the speed. I liked that. I can answer questions faster now.
"It gives a different name to the school. Other people come up and say `Well done'. No one says anything bad. No jealousy. Just `Well done'."