We are writing this on a coach. In an hour or two we will be in London, joining between 200,000 and a million people (depending on who you believe) to protest against the British army’s involvement in the war on Iraq.

Quite a change from yesterday when we spent most of the day in school or college. But not so different from Thursday, when we walked out of lessons to join an illegal roadblock in Cambridge where 17 people, most of them sixth-formers, were arrested. Or the previous college walk-out on March 5, involving around 300 sixth-formers. Or the demos we joined on September 28, February 15 and March 8.

Obviously the war is an issue that we feel very strongly about. But why are we spending so much of our school and free time campaigning, when we are not even old enough to vote? Why are teenagers around the world some of the most dedicated anti-war protesters? Why, when for years the Government has complained about the political apathy of young people, are school walk-outs and protesters as young as 13 filling the news?

The idea that our world was changed by the events of September 11, 2001 is, we believe, a simplistic cliche. But when the 911 attacks led to the bombing of Afghanistan, the “war on terror” and now war on Iraq, it did turn some teenagers who watched the destruction of the World Trade Center on TV into dedicated anti-war activists - even if they did have GCSEs to worry about.

Why do we protest? Because it gives us a voice. Because we have less to lose than adults. Because we’re still young and idealistic enough to believe that if we shout “Freedom for Palestine” enough times it might actually happen.

Because we’re scared - not of terrorist attacks here, but for the thousands of Iraqi people who don’t share our right to free speech and demonstration, and are being needlessly killed.

And because it’s fun. It really is. We may block the streets because we’re so angry at our country being dragged into this illegal, unjust war. But once we’re there, we can laugh, sing and invent an endless string of chants containing dodgy rhymes for “war”.

Of course some students may be attracted to spending Monday afternoon on a march instead of trying to calculate the cubic root of 457.83 (which incidentally is 7.707284948. No one can say missing school to protest has damaged our education). Schools, predictably, are not always enthusiastic about pupils who think the state of the world more important than exams.

That said, our school and college have been much more reasonable than some.

We have been allowed to hold meetings on school premises and students with parental permission have not been punished for participating in walk-outs.

Our schools have to be officially neutral, but individual teachers have been supportive.

We believe our actions and opinions are no less valid because we are of school age and cannot vote. We believe young people should not be marginalised or overlooked in society. Most of all we believe that the work of the anti-war movement is even more necessary now than before the war started. We will continue to work for peace and against the bullying of small countries by superpowers. We will try to ensure that a war like this can never happen again. But right now we have to go and finish our coursework.

Hannah Goreing, 16, is a student at Hills Road sixth-form college, Cambridge. Rachel Goreing, 14, is at St Mary’s school, Cambridge. These views are their own