Firstly an explanation. Students: the last day of school. You've now been in school for 13 of your 18 years - that's 72 near on 73% of your life. If you expect to live to 60, then that's going to be near on 20% of your life (not counting university). And it's the last time that all your friends are together - of course some of them you will keep in contact with, but not all. And of course, there's tradition. Something lasting needs to be contributed to the school; this is the prank. Something funny and witty, something interesting, something memorable.

What could be better than to look back later in life and reminisce with some friends about the time someone put all the bins in the school on top of the roof, or when so-and-so accidentally set fire to the school hedge and the field beyond when he followed the advice of his geography teacher and set fire to his geography books. And that's the importance of the prank. The final one, the big one. Life from now on is serious, so one last 'hurrah!' is necessary.

Several important rules must always be observed:

The prank should not cost anything to undo. If it does, it should be paid for by whoever did the prank, so it's just not worth it. Also, thought must be spared for anyone who has to clean it up (such as the caretaker or the janitor). You should really clean up the prank yourself.

No copying any previous years. This means that the prank must be original. Of course this only counts for an individual school, as otherwise there would be no way each school year could come up with individual plans.

Pranks should be not be offensive, and should have taste.

Research the target and have a well thought out plan in advance. No last minute plan is going to work. All effort and time put into advance planning will be well rewarded.

Don't tell anyone not involved with it.

A successful prank goes through the following stages:

• Plan
• Research
• Reconnoitering
• Action
• Observers
• Being caught
• Cleaning up

Let's go through a case study to explain all these points. A group of ten or so people decide to play a prank on a school (all aged in the age range of 17-18)¹.

• Plan - The plan is to paint a side of the mobiles² pink, so when the students come into school in the morning, the first thing they see is pink mobiles. The mobiles were originally painted green (as this was the 'official' school colour). And, incidentally, the plan was to paint it in emulsion so it could be easily washed off when the administration finally saw it.

• Research - The caretaker³. Now, this guy is hard working, and the day before leaving time, there was an event lower down the school. The caretaker had to spend time clearing away the tables and resetting the hall for exams for the next day. The other thing about the school was the security system. This school wasn't a very secure place (but then again, few large public facilities are). Anyway, you should make sure you know about the security system ahead of time, to avoid any nasty surprises.

• Reconnaissance - After the caretaker was observed leaving, the leader of the group went for a quick reckon, all seemed clear. Time is now around midnight, and the group made their way into school, scrambled the fence, and made their way over to the mobiles. It's usually right about now when things begin to go wrong.

• Action - Firstly, the group found the prank of the other, less responsible group of sixth formers. Now this is a bad thing - this vandalisation had to be cleaned up quickly, so the group set to work, cleaning the gloss paint of before it dried. And this is their main failure, setting them back by at least an hour. Once this was done, they then moved on and started painting the mobiles in emulsion (note the difference).

• Observers - Now, this is an important piece. Idealistically there should be no observers but there may be problems with this, and you get seen by someone not 'in the know'. But observation isn't what causes the problems - it's the reaction to the observation that ruins everything. This can also be a consequence of bad research. In this example, an unknown variable threw a spanner in the works - the milkman. He appeared at three in the morning. The group scattered (being quite a distance away) and hid - well, all but one. This caused the milkman to be concerned. Five minutes later the cry 'the Feds have arrived' rang out across the site, and the entire thing is abandoned, all parties fleeing and hiding.

• Being Caught - You will be caught. No matter how great the plan, you will be caught. However, when the police arrive at the site of this prank, they looked around and one pointed out to the other one a student 'hiding'. This guy, true to his every day form, realising that he's been caught, immediately gives in - and apparently his words, which should now become immortal are 'Can I help you officer?'.

  Well, that's it really - you would have thought that the prank was done for, but no, the police, with this guy's quick thinking (and indeed talking) quelled the police officers, so that they would not arrest them, but left them in peace to continue the prank. And of course, in the morning, the prank has the effect it wanted.

Amusingly enough, this prank provoked a surprising reaction from the teachers - most of whom were expected to complain that it demonstrated a severe lack of responsibility, that it's not what's expected from people of their age and that they should be setting an example to the rest of the school, etc. No, this time however, they said, 'Do you think they'll let us keep it?', and 'Can I have mine orange next time?'

• Cleaning up - Sure enough, the people owned up to it - or at least the guy who got caught did. And by the end of morning registration, there where seven or eight guys out there⁴ with buckets of water washing it off. And indeed, by the end of the first lesson, it was mostly gone.

A successful prank? Yes. No effort by the staff or extra expense was needed to clean up. Nobody got hurt, everyone found it funny, and everyone had a good time.

But don't assume that all plans will work. One suggestion was to electrify the bike sheds, and stick a mildly offensive notice up, then when the deputy head comes in, he reaches to take it down and an amusing spectacle occurs. Not a good idea, for obvious reasons.

And to students out there: stick to the guidelines. Don't do anything that you couldn't clean up or get out of. And selling the deputy head's car really is not worth it. Funny, yes. Worth it, no.