Of all the roles I thought I might play as a classroom teacher, it never occurred to me that I might be called upon to be a spook. Social worker, surrogate parent, cleaner, technician, crowd controller, salesman for the damaged goods of the national curriculum, yes – but I never imagined I might be required to be a quasi-MI6 agent, snooping around the playground for budding terrorists. Yet this is what the government is calling for state school teachers like me to be; government guidance published today will ask teachers to monitor pupils' behaviour and inform the authorities – including police – if they suspect teenagers are being drawn into violent extremism.

As with much of the guidance that the government provides teachers, it is highly contradictory. On the one hand, it encourages teachers to discuss the issues surrounding terrorism – the threat from extreme Islamist groups, al-Qaida, and other fanatics hellbent upon blowing up innocent citizens – which seems reasonable enough. But on the other, the plan aims to extend the "in loco parentis" responsibilities of teachers to monitoring whether pupils are becoming extremists and telling the authorities. This begs a couple of questions. Surely, if pupils know that teachers are obliged to report them if they articulate their extreme views, then they'll be very cautious about saying anything that might incriminate themselves? Furthermore, won't it inhibit any discussion from those pupils – or teachers for that matter – who are not extremists but have some sympathy for "freedom fighters" who advocate violence – such as Nelson Mandela?

I am currently teaching Chinua Achebe's Things Fall Apart, which is about an African man's violent and ultimately suicidal response to British colonial rule in Nigeria in the 19th century, and fielding all sorts of left-of-field comments from my sixth formers, some of whom are suggesting that the African is right to take up arms against his oppressors, even though it's clear he's on a suicide mission. Should I be reporting these impassioned, engaged students as potential fodder for al-Qaida? If the pupils knew I might, all sensible discussion about the novel would cease.

Perhaps even more pertinently, I have taught pupils after 9/11, and during the Iraq war, who have expressed sympathies for both Osama bin Laden and Saddam Hussein. On both occasions, this has provoked a furious response from the rest of the class and a lively, impassioned debate has ensued; the sort of debate about religious fundamentalism, freedom of speech and changing the world that the Secretary for the Department of Children, Families and Schools, Ed Balls, wants lots of teachers to conduct throughout the country. However, I am pretty sure that they wouldn't have happened if the pupils who provoked the discussions with their defence of al-Qaida and the former Iraqi dictator knew that I would have to report them to the authorities. Interestingly, in both cases, these pupils were clearly not budding terrorists, but what I would call clever "wind-up" merchants who relished putting everyone's backs up.

However, I have come across some characters at school that I have suspected of being serious fanatics. Funnily enough, they weren't pupils but teachers! These pedagogues were not the sort of bombastic, careless blusterers who trigger great classroom discussions but quiet, devout teachers who were obviously very religious, praying every day and wearing the appropriate garb. While I might have suspected them of harbouring dreams of violence, I had absolutely no evidence of it, beyond their belief that homosexuals should be executed. They certainly were very careful not to talk about Bin Laden or al-Qaida. I had a gay colleague who was so incensed when she questioned one of these teachers about their attitudes towards homosexuality that she did complain to the authorities. She was quickly silenced with the response that it was a religious matter – and no action was taken. Indeed, that fundamentalist teacher went on to pass his trainee year and now is teaching at a state school as a fully qualified teacher.

This has made me think that perhaps teachers need to be properly vetted before we turn our attention to the pupils. After all, one of the 7/7 bombers was a primary school assistant; it is possible, he could well have been rooted out if properly questioned about his attitude towards violence in a job interview. Perhaps he would not have blurted out that he wanted to be a suicide bomber, but his attitudes towards homosexuality could have been fairly easily discovered. Personally, I think that anyone who believes that gay people should be exterminated should not be allowed to teach our children. The government, though, seems to reluctant to deal with this thorny issue and instead wants to turn teachers into ineffectual spooks, which will have the effect of stifling all meaningful debate.