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For the past few months I've been engaged in a top-secret study that will radically affect the future and has taken a grip on my psyche. It's called How Best to Secure a Half-Decent State Education in London: special focus - my son, 5 next birthday. Now, with the application forms in, I can tell all. The conclusions are surprising.

When last September I came back to Greenwich, in southeast London, from France, where we'd been living, I was a primary school virgin. I didn't have the benefit of NCT (National Childbirth Trust) friends, or any other network of local mums who might provide useful information.

All I knew - and it was not encouraging - was that last year primary school results in Greenwich were the fourth worst in Britain. I did, however, have one advantage: a friend who works in education for an Inner-London authority who has developed a sophisticated strategy for choosing schools for her children. As I embarked on the research project, which is what applying for a primary school place becomes, she warned me to be vague when talking about it - so other parents didn't pip me for a place in a school they might not have considered. I must impart only what I'd found once the deadline for applications had passed. “You have to be very scheming,” she said.

I soon saw what she meant. As I pored over league tables, Ofsted reports, prospectuses and information booklets, other mothers were talking about moving to the catchment area of Greenwich's best school. They were prepared to move from green leafiness to a thundering flyover and to pay a premium on their house for the privilege. That wasn't for me. I'd just sold a house in France. My mental health couldn't take it again.

Other families were religiously attending church - but not necessarily with religion in mind. That was unlikely to help me: the SATs results of my local church primary school were uninspiring. Attending a church farther away that feeds into a good school would be too obvious. I couldn't do it. I was amazed at the antics. A careful review of all the information and a bit of logic showed that there was no need to panic.

I decided I wanted my son to go to our nearest school, a five-minute walk away. It is popular with active parental involvement: not at the top of the league tables, but not at the bottom either. “It's lovely,” said my son's nursery-school teacher, who once worked there. It's a real community school - a bonus for a lone parent like me with an only child - and we wouldn't have to get a bus or drive the car to get there. But its popularity has shrunk the catchment area.

Of the next nearest schools to our home, one is so small that it took no one last year unless it was their closest establishment. Another is the local church school and the other is a sink primary close to the bottom of the borough rankings. This, as we already know, is saying something.

The tiny school, pretty much a hope-free zone, was an obvious second choice. “Include the faith school too,” urged my educationist friend. “It doesn't matter that you don't go to church - it was undersubscribed.” I resisted the sink school, even as a last choice. “Put it down!” my friend cried. She made me realise that if I didn't include it anddidn't get a place elsewhere, the council might choose a worse school for me. She pointed out that if my child did end up at the sink school, I would almost certainly be able to move him to another school of my choice a year or two later. Places at popular schools become available as parents move.

The other thing not many people know is that you are not restricted to one borough. And the boroughs don't compare notes. “You could end up with two places if you apply to two boroughs,” the lady in Greenwich's admissions office confirmed. I was greatly cheered, especially as nearby Lewisham has better schools.

I recklessly listed one of Lewisham's most popular and successful schools as my top preference in that borough. It would take a miracle to get in, but I had nothing to lose.

And then I found it - the hidden gem that every parent hopes for. In rundown Deptford was a Lewisham primary school that last year came seventh in the country for “value added” - how much it brings its pupils on in the time they spend there - and is this year once again on the list of the nation's top schools for pupils' progress. Its Key Stage 2 results are better than those of any of the schools I have selected in Greenwich - amazing given that seven years ago it was in special measures and 66 per cent of its pupils have a first language other than English.

Yet no parent I've spoken to in my area knows of Tidemill Primary School. What's more, last year it offered 41 places out of 60 available, despite having 91 applicants. Clearly, many parents gave it low priority on their preferences and ended up with a place in a higher-choice school.

This may be partly because middle-class parents don't apply. They're unlikely to come across like-minded mothers there. As one father said to me: “It may get good results, but it's full of oiks.”

Mark Elms is the head who took over Tidemill in 2001. “It was a poisoned chalice,” he says, but he has turned it around with his entrepreneurialism (he has raised £18 million to build a new school) and uncompromising approach (he fired 80 per cent of the staff when he arrived and forces parents to attend workshops once a half term). I was impressed.

I'd have a hard job choosing between my neighbourhood Greenwich school and the one in Deptford if my son got places in both.

But I'm one of the lucky ones. What about the mother of one of my son's nursery-school friends? She has applied to only two schools, both boasting respectable results, both oversubscribed - and neither is her nearest school. Her closest is one of Greenwich's worst and she'd rather die than include it on her form. But she'll probably end up with a place there, because both her preferred primaries are so tiny that the chances of her son getting in are minute. Yet she lives a bottle's throw from much larger Tidemill and hasn't listed it.

And that's the tragedy, really. It's too bad if the middle-class parents don't find this school. They'll get by somehow. It's the people who want the best for their child but don't understand how to analyse the welter of information, who don't have a friend in education, who don't realise that it's hopeless putting a top-performing school on their list when they live miles away, who will get a rubbish deal. No lottery - except perhaps the national one - is going to help them.

As for the rest of us, we of the sharp elbows and cunning plans, let's just chill? At least until May 2, when we find out what school we've got.

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