I am walking down the corridors of Sir John Cass secondary school in Tower Hamlets and it feels very weird. I am not dodging missiles, hearing abuse or witnessing scraps between children. This seems a totally different school from the one I taught at during the early 1990s; there isn’t a fight in sight, not a shred of litter and the school now has some of the best results in the country, instead of the worst.

Since Sir John Cass is near where I live, in east London, I am thinking about sending my son here when he is old enough in a few years’ time. Its recent Ofsted report rated the school as "outstanding" and it is considered to be one of the most improved schools in the country. So here I am at the annual open morning, listening to the headteacher, Haydn Evans, as he guides parents around the site, describing the school’s "faith-based" ethos and firm discipline.

Everything we see in the classrooms confirms this. As we are walking around viewing the gleaming new facilities, a smart-suited parent tells me that a lot of his friends have moved to the countryside in search of good schools, but now he realises that they wasted their time. "This school seems far better than any of the ropey old comps in the suburbs!" he chortles.

Many of the parents are anxious, asking questions about the school’s results, how it deals with bullying, its extra-curricular classes. I am very familiar with their concerns because as a teacher I have fielded numerous similar questions during open days since leaving Sir John Cass secondary.

At the comprehensive where I am currently a head of department, I watch the parents stalking around, clutching their bewildered children and their notebooks. They could be intoning the mantra: "We’re going on a school hunt, we’re going on a school hunt!" Their eyes scan every gleaming piece of display work, every book they can lay their hands on, every computer, every Bunsen burner.

This is the open day season for year 5 and 6 parents. Many parents are bamboozled by the process. Most boroughs will hold evenings at primary schools explaining the complex processes involved, but many parents remain confused. Few understand properly the admissions rules for secondary schools, and fewer know how to spot a good school, preferring to rely on myths rather than facts.

Before parents start schlepping around lots of schools, it is worth spending a few minutes on the internet. Log on to schoolsfinder.direct.gov.uk and, simply by typing in your postcode, you can see which your local schools are. You can read the Ofsted report on each, which will provide an overall judgment on the school. The Ofsted report will be more reliable than reading the raw data in the league tables, which won’t take account of the type of pupils entering the school.

Some believe that open days can be misleading. "Parents should make sure they go along during lessons and see how the teachers behave towards the pupils," suggests Huda al Bander, 19, a veteran of London comprehensives and colleges. Al Bander is among a group of teenagers belonging to the Edge Learner Forum, a unique organisation working to promote practical learning in schools.

"A good school is a school where you will see teachers not only talking to the whole class but also working one-to-one with the pupils, listening to their questions and not putting them down," she says. And "good schools cater to pupils’ different learning styles, and the best schools get the right balance between practical learning and theory". Increasingly, educationalists are realising that pupils learn effectively in different ways and need chances to learn through dance, drama, art, music and doing presentations.

Edge Learner Forum members warn against selecting a school just because the child’s friends are going there. "They are only 11 and they will make new friends very easily."

I have spoken to several parents who have sent their child to schools precisely because their friends are not there. Don’t be blackmailed by your child on this issue. Choose the best school, not the most sociable one.

Many parents are confused by the number of different types of secondary school that exist: academies, city technology colleges, specialist schools, special schools, faith schools, local community schools, pupil referral units.

The differences between them may be many, but the essential point is that they should all be judged on the same criteria: their academic record, particularly in English and maths; their most recent Ofsted report; the behaviour and attitude of the pupils; and their extra-curricular provision.

The final decision should rest with the parent, but it is worth involving your child in extended conversations about where they should go to school, discussing with them your ambitions and hopes. Keep the conversation positive.

Negative opinions

Equally, if you realise that your child is going to be sent to a school that you think is rubbish, you should try to keep your most negative opinions to yourself because they could affect your child’s whole experience of the school. This is going to be increasingly important because 21% of parents don’t get their first choice of school. The government recently changed the law by which schools can admit students so that the majority of parents will have to choose from schools in their local catchment area. The rules remain complicated and there are some exceptions. Most important is to read the admissions criteria very carefully.

During the open evening, it is worth listening to the admissions part of the headteacher’s speech and getting him or her, or someone else in the know, to explain it to you again if you don’t understand it. This could save you an enormous amount of time and effort later: the last thing you want is to apply for a school at which your child can’t possibly gain a place. Your open evening may be the last chance you have to talk to someone in the know about admissions criteria.

Finally, once you’ve chosen your schools, make sure you fill in the forms correctly. Some schools – faith schools in particular – require that you send an application to them and one to the local education authority, while other schools require you to apply only through the local education authority. Again, checking this at an open evening saves much agony.

It is also worth finding out the best way to rank your schools on your form. Many local authorities, including all those in London, operate a policy of offering one school place only, giving parents their highest ranked school with places. This means that if a parent has put top of their list two schools for which their child does not meet the criteria, then if they met enough of the criteria they would be offered a place at the third school. Should you be given a third place, but you are not very happy about it, you can appeal to the first two schools. If you don’t meet the criteria for any of the schools on your list, you will be given the nearest school to your house with spare places — often a very unpopular school which is miles away!

Happy hunting

The main thing to remember is that ultimately it is not the school that makes the real difference: it is the parents. Even if your child goes to a school you would never have chosen, given the right support at home he or she will succeed. However, if you do hunt down a good school and get your child into it, you’ll be saving yourself much work and stress in the long run. If your child is not being properly taught, you’ll need to fill in the gaps by either teaching them yourself or hiring private tutors. Happy hunting and good luck.

· Francis Gilbert teaches English at a mixed-sex comprehensive in outer London. His book, Parent Power: The Complete Guide to Getting the Best Education For Your Child, is published by Piatkus

Killer questions for the open day
Ask teachers:

Would you send your child to this school?
What would you do if I complained that my child was being bullied?
How does the school cater for gifted and talented children?
What evidence can you show me that my child will be stretched?
How does it cater for children with learning difficulties?
What would you do if I complained about the quality of teaching?

Ask pupils:

What level/grades are you in English/maths/science?
What do you have to do to improve in these subjects?
What are the best things about lessons?
What are the worst?
How well behaved are the children?
What does the school do with bullies and disruptive pupils?
What are the dinners like and are the toilets kept nicely?

League tables: which bits are important?
Read with caution

Don’t trust the school league tables fully. The fiasco of this year’s Sats, which meant that many papers were not marked properly or went missing, will delay some league tables by several months, the government announced last week. But even the league tables that were published this year need to be read with caution. To use them properly you will need to look behind the headline figures. In particular, check the maths and English scores at GCSE. If the school is getting below 50% A*-C grades in these subjects, it means that more than half the pupils are not leaving school with the required minimum standards. This may not be a problem in a school where the majority of children have English as an additional language, but if that is not the case, be wary. Look also at the numbers of children gaining five "good" GCSEs: in English, maths, the sciences, and modern foreign languages (MFL). Some schools may not offer much in the way of languages or sciences at GCSE. They should. At Sir John Cass, all the top achieving students are given the chance to study "triple" science – physics, chemistry and biology – and a host of languages.

Check the value-added scores

Does the school add "value" to the pupils? Schools that score below 100 on the league table present a problem because they are not helping their students to learn at a rapid rate; the students are merely trotting along at their expected levels or below, and are not achieving over and above what they could achieve.

Find the Ofsted report

Do read a recent Ofsted report. They often give precious information about whether a school really makes a difference to a pupil’s attainment. In particular, the Ofsted report will give a clear picture of the standards of teaching and learning in the school overall, rating it from 1-4, with 1 being outstanding, 2 being good, 3 being satisfactory and 4 being unsatisfactory. Any recent Ofsted report that rates the standards of teaching and learning as "satisfactory" or below indicates that the school is a bit mediocre. Similarly, the Ofsted report will give a ranking from 1-4 on the school’s overall effectiveness, the behaviour of the pupils and a host of other areas.

Special educational needs

Check how many pupils are on the SEN register and the provision for them. If there are more than 40% of pupils on the SEN register, then I would investigate the school very carefully; this means that more than a third of pupils have learning difficulties. Does the school have the trained staff and SEN teachers to cope with so many SEN pupils? What facilities does it have to help them improve?