History is scattered with examples of school students throwing themselves into political causes and taking their fight to the streets — think the anti-Vietnam movement and the March for Our Lives rallies in Washington.

On Monday, Prime Minister Scott Morrison made it clear how he felt about Australian students taking time off school to protest.

"We don't support the idea of kids not going to school to participate in things that can be dealt with outside of school," he said.

"We don't support our schools being turned into parliaments. What we want is more learning in schools and less activism in schools."

This week, hundreds of students around the country are ignoring that advice and heading to Student Strike for Climate Action rallies — Canberra held one on Wednesday, Hobart's was on Thursday, and other capitals held theirs on Friday.

Experts say taking part in activism is "all part of a civics education".

It's hard to put an age limit on activism, experts say. ( ABC News: Jack Tegg )

What's the impact of activism on kids?

Psychologist and author Steve Biddulph said student activism had very real mental health benefits.

"Scott Morrison is diametrically wrong on this one," he said.

"Many children and teens are affected by the state of the world with climate and cruelty to refugees and the environment generally topping the list.

"Involvement in helping the world is the key to mental health and making good adults for the future."

US student and activist Emma Gonzalez made waves internationally after the Marjory Stoneman Douglas High School shooting. ( Reuters: Jonathan Ernst )

Professor Michael Platow from the Australian National University's Research School of Psychology agreed.

"It's all part of a civics education, it's getting students engaging in their civic responsibility," he said.

"Schools need to go beyond teaching maths and science because it's part of a student's role to engage — they're required by the state to engage.

"Any democracy wants to replicate itself in the next generation, we don't want demagogues to come in, we want a citizenship that embraces and engages with a vibrant democracy."

He said adults shouldn't let their own views cloud their judgment of their children's political or social activities.

"We have to separate our own personal values about the topic, from the process of engaging in civic activity. We can disagree with the topic but we can't disagree with the process."

How young is too young?

School students were a key part of the March for Our Lives protests in the US. ( AP: David J. Phillip )

Kevan Goodworth, chair of the Australian Council of State School Organisations, said age was "complex".

"I think it's more something that you would not imagine a younger person of five or six years old necessarily might have an interest in," he said.

He said while some kids just wanted to skip school, most were genuinely engaged with the topic.

"We would almost always find a situation where one or two students saw this as a day off school, but that's certainly not something that I am hearing from the passion being evinced this morning from the students who are taking a stand," he said.

"We encourage the situation where parents and children are talking about these matters around the dinner table in the home and coming to considered opinions."

What about the time off school?

The student rallies are being held around the country. ( ABC News: Jack Tegg )

Rules about school absences vary from state to state.

In New South Wales, Education Department guidelines say principals may grant attendance exemptions for things like participation in elite sport or "employment in the entertainment industry", but other activities have to be referred up.

In Tasmania, even with parental permission a student's absence will be marked as "unauthorised" unless they are at a recognised state, national or international event or are "participating in a recognised learning experience".

After an unspecified number of unauthorised absences the school will send a letter home asking for an explanation.

Ultimately though, parental consent is the key.

Nelson File — the principal of the Friends school in Hobart — said he would prefer it if rallies were held on weekends, but that he supported students attending as long as their parents got them there and back.

"The goal of our school is to have students develop into adults who are actively engaged, who understand what the issues are and think about the kind of society they want to live in," he said.

"We want students who think clearly about how to create a more just society."

'The PM's not doing anything, so we have to'

The rallies were held in Canberra on Wednesday, and in Hobart on Thursday. ( ABC News: Jack Tegg )

At today's protest in Tasmania, student Amelie Hudspeth said she would not need to miss school if the Government was doing its job on climate change.

"As young people it's really important to us that we have a safe future, and at the moment it's just not happening," she said.

"[The Prime Minister said] students shouldn't miss school for anything that could be dealt with out of school, but he's not doing anything so we had to."

Woodbridge school student Imogen Viner said: "Without activism there's not point in going to school because there won't be a future we want to live in.

"Australia used to lead the world in renewables and now we're not doing anything."