However challenging this stage of life might be for young people and those who have to deal with them, these signs are known, they are obvious, and they have been around for generations.

But scientists are now focussing on an earlier hormonal surge that happens at about eight years of age, which they believe has significant implications for children's social and emotional well-being and also sets the stage for the main event of physical puberty a few years later.

Known as adrenarche or adrenal puberty, it has no obvious external traits - it does not, in its early stages, cause any physical changes in a child - but the hormones involved affect how children relate to their families, teachers and peers. Researchers now believe that it is a more significant time in a child's development than previously thought, which in turn may force us to rethink not only how we raise children, but also how we educate them.

While scientists have been aware of adrenarche for some time, little is known about the precise function of these adrenal hormone changes, which is one of the reasons behind the biggest longitudinal study of puberty in Australia, the Childhood to Adolescence Transition Study. A joint project between the Murdoch Children's Research Institute and the Royal Children's Hospital, the study follows 1200 children from year 3 onwards, looking at the entire scope of puberty and the effect it has on all facets of young people's lives. Using questionnaires, saliva samples to measure hormones and some physical measurements such as height, weight and waist circumference, the study also examines exactly when children reach each stage of development. Researchers hope to understand why children are entering physical puberty much earlier than in previous generations.

Already there have been some interesting findings from the research, now in its fourth year. For instance, the idea that seven to nine-year-olds are in a quiet or "latent phase" of development has already been turned on its head, says lead researcher Professor George Patton.

For example, MRI scans on a sub-group of students have shown that boys who enter adrenarche early have significantly different brain patterns from those who do not.

"We are undoubtedly seeing patterns of brain activity as well as the emotional and social world … is also different from those who have not yet started," he says. The parents of these boys have also reported higher incidence of behavioural problems.

Patton says the experience of boys and girls in puberty is vastly different. For girls the onset of "puberty proper", which starts with breast buds and eventually leads to menstruation, tends to have a much bigger impact on them than adrenarche.

"As girls go through the process of gonadal maturation they report a lot more troubles with emotions such as anxiety, unhappiness and stress," he says.

To teacher Catherine Coley, the idea that adrenal puberty might be more significant than previously thought makes a lot of sense. North Melbourne Primary School, where Coley teaches year 6, is one of the schools involved in the study, and she has given much thought to how it all affects her students (last year she taught the year 4/5 class involved in the study, so has tracked the same group of pupils through their involvement.)

She has noticed that, in year 4 in particular, something starts to shift: children can have unexpectedly emotional responses to issues, and friendship groups become a little more intense and fractious.

"I would say in about 90 per cent of kids you see emotional changes before you see the developmental stuff," she says. "You can tell there are emotions, but they don't know what those emotions are."

She is also not surprised that  boys seem to be more significantly affected than girls at this early stage.

When the physical changes start to happen, the difference between those who have started puberty and those who have not can be huge, she says.

Coley went through puberty early herself: she was a tall, physically mature girl and started her first period at the end of year 3, and says age 10 and 11 were more difficult for her than the teenage years because of all the hormonal changes she was dealing with. So she knows how difficult puberty can be for a young person generally, and how awkward it can be to discuss.

"Kids are just so curious and they want to know, but I think they find it difficult to talk about," she says. "They feel like there's something wrong with them when it's a completely normal thing."

Gemma, who graduated from North Melbourne Primary last year and is starting year 7 next week, says it's pretty obvious who has hit puberty and who has not. And no, it's not the easiest thing to talk about. "It's pretty awkward," she says shyly. "I don't feel comfortable talking to my older brothers about it. I feel much more comfortable talking to my mum about it."

Gemma's mother, Cathy Robinson, says: "Certainly Gemma is quite happy to talk to me, but my boys are less likely to talk to me about it."

Her eldest son was interested in his sex education classes, whereas Gemma is more inclined to worry about how it might affect her.

"We're quite open, so we would talk about it if it came up," she says.

But long before those first hairs begin to sprout, there is much more going on than previously thought. Dr Lisa Mundy, another researcher on the CATS team, says the findings on the significance of adrenarche overturn the idea that this is a developmentally "quiet" time for children. In the years leading up to the onset of physical puberty, the groundwork is being laid for children's identity and social connectedness.

"This is a huge time of change, because they're gearing up for secondary school and there's obviously a lot of worries and concerns about that," she says. "There's obviously a lot going on at a biological level as well. Their relationships with their peers, changing relationships with their families, their school, and all of this is happening at a time when their biology is really changing."

Adrenal puberty is in some ways the precursor to physical puberty - the hormones that surge during adrenarche are the same ones that later create pubic hair, sweatiness and acne in girls (breast development and menstruation are governed by different hormones). For some years now, there has been concern that children seem to be reaching puberty earlier and earlier - walk through any primary school and you'll see girls who already look like young women.

But is this really happening and if so, why? Patton says there is no doubt that, over the past couple of hundred years - particularly since industrialisation - there has been a steady decline in the average age of the onset of puberty, and particularly of menarche, or a girl's first period. But that has actually plateaued in the past couple of decades, hovering at about 12 years (for boys, puberty happens about a year later, and is usually marked by their voices breaking).

The most significant reasons behind that steady decline in age are the control of childhood infection and better nutrition. Evolution underpins much of the biological evidence for puberty: for example, researchers believe that bigger children will reach puberty earlier because the body feels it is "safe" to mature. Therefore obesity becomes a risk factor for premature puberty.

Many parents no doubt accept that puberty happens when it happens: there is, after all, not much they can do about it. Nonetheless, there is constant concern about the gap between a child's physical development and their social and emotional development.

That certainly worries Cath Taylor, whose two daughters attend North Melbourne Primary, this year entering year 5 and year 4. "[It's] not so much puberty but the growing up too fast. But it's something that you try to head off as much as possible," she says.

Taylor feels comfortable discussing puberty with her children, she says, and will do so from time to time - she has already had discussions with them about the difference between boys and girls, for example, and "I think they would feel like they could come and talk to me about it."

For those children who do reach physical puberty ahead of their peers, it can be a difficult time.

While the connection between physical health and weight and the onset of puberty has been known for many years, there is now compelling evidence that a child's social environment can also have an effect. For example, girls who have traumatic childhoods, or who are living with a non-biological male (a stepfather, for example) are more likely to go through puberty early than those who do not. Again, there seems to be an evolutionary trigger, a biological impulse to survive by reaching adulthood sooner.

Does it matter? Well, probably not for most people, but on a population level, there is evidence that early puberty can have health implications for young people later in life, says Patton.

For example, girls in particular appear to be at greater risk of some cancers, including breast cancer, later in life, and there is an increased risk of adolescent mental health and heart disease later in life.

But Patton says early puberty is "just one of many risk factors for these problems and those risks can be reduced by supporting a child well and establishing a healthy lifestyle that continues into adolescence and adulthood".

While it may not be the case that children are entering physical puberty any earlier than their parents, Patton says the vastly different social environment in which they are growing up raises concerns about that gap between physical and emotional maturity.

That is why it is important that more attention be given to the long and complex pubertal process, starting in the middle primary years.

"This is a complex transition that these kids are going through," Patton says. "Their identity, their sense of self is emerging. The biological processes of gonadarche and adrenarche are driving this forward, but where children are getting this from is about the social and emotional context in which children are living."

So the implications are significant for how we raise and teach children in this age group, he believes. We should no longer think of this as a quiet period between toddlerhood and adolescence, but as an important time of emotional and social development that is driven by a strong biological imperative.

"The policy of 'benign neglect' that has characterised our approach in the past is probably something that we can no longer afford. With so many new influences, including marketing and new media, we need to be thinking much more proactively about the social, emotional and learning environments we are creating for our kids during those years."

The three stages of puberty

ADRENARCHE: Also known as adrenal puberty, this is the first cascade of hormones that usually happens at about eight years of age. Although there are no obvious physical signs of it beginning, researchers believe it heralds a new phase of brain development that affects identity and emotional well-being.

When physical puberty kicks in, these androgens are responsible for the development of pubic hair, sweatiness and acne in girls.

GONADARCHE: Traditionally the time thought of as puberty, this is when the sex hormones estrogen and testosterone surge, causing physical maturation. For girls the first signs of this stage are usually breast buds and pubic hair; for boys the onset is more marked by body odour and pubic hair.

GROWTH SPURT: This usually happens when puberty is well under way, about 12 years for girls and 14 years for boys.