Their combined age does not even come close to how many years Keith Richards has been on the planet, but four girls in Grade 4 are already mastering their rock-star poses.

The drummer is hunched over her kit, ready to hammer out a driving beat; the bassist, her face partially obscured by a scarf, has her guitar slung nonchalantly over her shoulder; the singer bestrides her mic stand and clasps it with both hands. The shy smiles, though, are those of 10-year-old girls - there’s work to do on the anti-authoritarian snarl.

What is more unusual than this unorthodox primary school band, however, is the adult supervision - there isn’t any. These girls can practise on their own before, during or after school, as long as there is no clash with lessons. “They can come in here when they feel like it, as long as somebody is working somewhere in the school - we trust them,” says teacher Juhana Pohjanpalo, a Grade 4 teacher at Vierumaki Comprehensive in Vantaa.

Along the corridor, Mr Pohjanpalo has just been teaching his fourth-grade class. He wears an ear-ring, faded black jeans and a T-shirt emblazoned with the logo for Canadian punk band Sum 41 (sample lyrics: “I’ll never fall in line, Become another victim of your conformity”).

When I ask principal Pia Aaltonen if there is any dress code, she returns a quizzical look. Teachers - and pupils - know not to take things to extremes, but there are more important issues to worry about than clothing.

Strictly-applied regulations on behaviour and appearance of the 22 teachers and 386 pupils (aged six to 12) at Vierumaki are at a minimum: both are trusted to use their time productively, unhindered by fussy strictures.

There is huge trust, too, in Ms Aaltonen.

Beyond a series of loose national guidelines, Finland’s 415 local authorities, within six provinces, are free to help schools fit with the local culture and environment. So the curriculum in a remote island fishing community will be quite different from an inner-city Helsinki school. The state is far more likely to issue edicts about health than the curriculum - all lower comprehensive (primary) pupils must eat a free balanced meal, provided on the premises, and vending machines are banned.

There is no national inspection system and individual schools come up with their own curriculum. Local authorities determine how much autonomy is passed to schools and, in Ms Aaltonen’s case, a huge amount of faith is placed in her ability to run this one.

“I am the only one who inspects the rooms and the teachers,” she says.

Each spring, she sits down with the local authority to discuss the school’s priorities and curriculum for the year ahead. One big priority just now is class sizes, which range between 20 and 30 for mainstream groups. The upper extremity is “too high” and Ms Aaltonen will be taking the matter up with local education officials.

“The most important decisions are made in the school - that is the system,” she says. “There are guidelines that come from the national board of education, but I think that the real work is done here. My role is I have a budget, I have a lot of money. Then I have these guidelines - how to use that money. But we decide things here.”

The buck may stop with Ms Aaltonen, but she is not an authoritarian or high-handed leader. She wants, for example, to experience the demands placed on teachers. So she teaches eight hours a week, in French, maths and English, time she believes is crucial to her smooth running of the school. “That is the way you get to know the children, and when you do the work of teachers you know how to guide it and other things in the school,” she says. “I think it’s very helpful. This is why we don’t need any professional managers.”

Parents play a central role in deciding how the school is run. A board made up of five parents and Ms Aaltonen meets four times annually, and approves the school plan each year. Parents can - and do - demand big changes to plans before signing up.

Meanwhile, a parents’ association - technically made up of all parents, although some are more active than others - has roughly 10 meetings each school year. Parents are also welcome to drop in unannounced to the school at any time and sit in on a class, although few choose to do so.

The lack of rigid hierarchies and strict school rules is matched by a non-punitive approach to discipline. Ms Aaltonen says detention is very rare in Vierumaki, although more common in some other schools, and knows of no child ever being expelled from any school in Vantaa.

“If something happens, we always arrange school negotiations where we ask children about things, and we might invite parents to come in,” she says. “We would never stop a child coming to school. We also don’t believe in making a child sit in a gym and staring - that’s ancient. Children must think about what they do, and by helping them think with their own brains you get the best results.”

Fifth-grade teacher Katja Eloranta adds that teaching is largely about helping children “make connections with others” and showing them how “to be with other people”.

A small but telling incident during The TESS’s visit to Vierumaki reveals how much staff can rely on the good behaviour of pupils. As we leave Ms Aaltonen’s office to visit a class, she leaves the door wide open. I look anxiously back at my bag, which is filled with a laptop, other electronic items and important notes, and sitting in full view of one of the school’s main corridors.

Ms Aaltonen picks up on my nervousness and reassures me: “Don’t worry, nobody will take it.”

The TESS is free to wander almost at leisure around the school, speaking to passing teachers in the corridor and dropping into classes that have not been handpicked and readied for our visit. Children are generally well-mannered and enthusiastic, but there are no heavy-handed attempts to drum out mischievous streaks.

Riitta Lindell, a teacher for 30 years, is using a digital projector to show a busy cartoon seaside scene for an English lesson on transport. There are only 15 pupils, aged nine or so, sitting in a Grade 3 class normally twice that size; teachers can negotiate for periods where they only have to take half a class. “It makes it much easier for us all to work,” says Mrs Lindell, who chooses to give all her pupils a couple of periods for both English and maths where they learn in the smaller group.

“What colour is the bus?”, “How many boats can you see?” she enunciates in a clipped English accent.

Niko and Lauri do not appear too interested and whisper apparently hilarious asides to each other; Lauri wanders away from his desk to fetch something; Niko casually flicks Lauri with his hand.

Mrs Lindell carries on with her lesson, relaxed about their behaviour but able to keep an eye on it, with fewer pupils than usual to think about. The volume gets a little higher at one point, and she quietly admonishes the boys without disrupting the flow of her teaching. Eventually, a frustrated Niko tugs at Lauri’s sleeve - his accomplice has started to pay attention.

Pragmatism is a virtue at Vierumaki. Half-classes, for example, are not assigned for a whole year in advance, but can change from week to week. In general, the more pupils and the younger those pupils, the more half-class time is due, although there are no hard and fast rules.

What works is what counts, as can also be seen in the school’s work with special needs pupils (there are 40 with clinically recognised special needs and 80 with other additional requirements). Despite a national move towards inclusion, special needs teacher Marianne Anderson and special needs classroom assistant Marianna Anttonen explain that they take a class of 12, where the children mostly work best away from the distraction of other pupils.

Such decisions are not made on a whim: also based in the school are a full-time psychologist (who divides her time between pupils and other people in the local community), a social worker who provides a connection with social services, and a nurse. They, along with special needs teachers and Ms Aaltonen, make decisions about how to divide resources and the level of special needs education required by each pupil.

The widespread lauding of Finland’s schools in the British media sometimes gives the impression that they are doing things radically differently. But in some ways, things are quite traditional. Classes in Vierumaki tend to be organised into neat rows with teachers holding forth from the front of the class, and one typical classroom has little to adorn its walls, save for a few homemade snowflake decorations and paper windmills.

Banal little scenes of everyday school life are more telling, however, than how a classroom looks. Without asking, pupils go to the toilet, leave the room at the end of a lesson, come to the teacher’s desk to sharpen a pencil while the teacher talks, pull their feet up onto their chairs, and go off for impromptu band practice.

The message is implicit but crystal-clear: pupils are trusted, they are responsible and they can decide things for themselves. Trust in others, from Mr Pohjanpalo’s willingness to leave the band on its own to the state’s hands-off approach, is the thread that runs through all levels of Finnish education.