It may be the smile - or the indifference - that greets you; it may be the noise - or even the silence.
Within minutes of visiting a school, you get a sense of whether it is a good one or a bad one. Whether it feels right for your child.
First impressions can be misleading, but nothing can replace dropping in at a school during a normal working day.
Equally, even the "best" school - however defined - might not be right for your child. As a parent or carer, you know your child's needs better than anyone.
Schools are important, but families matter even more; children spend only about one-fifth of waking hours in school. Even the best schools cannot compensate for the social and economic inequalities of the world around them.
Many schools in this guide should be performing better, given the relative advantages enjoyed by their pupils; equally, many that appear to be doing less well academically are achieving remarkable results for the disadvantaged communities they serve.
The starting point is the Brighton and Hove City Council website: www.brighton-hove.gov.uk/content/children-and-education/schools.
For data about examinations, the Department of Education (DfE) performance tables contain everything you need - and more: www.education.gov.uk/schools/performance.
It will be several months before data for 2014 is published by the DfE.
For fee-paying schools, the Independent Schools Council (www.isc.co.uk) is a key organisation, representing 1,200 schools in the United Kingdom and abroad - and bringing together eight associations of independent schools, their headteachers, bursars, and governors.
The main associations are: The Girls' Schools Association (GSA); Headmasters' and Headmistresses' Conference (HMC); Independent Association of Prep Schools (IAPS); and Independent Schools Association (ISA).
Inspection reports are the product of the Independent Schools Inspectorate, the body responsible for the inspection of schools in membership of the constituent associations: www.isi.net.
If your child has special needs, there are many agencies and organisations that can help. For a basic overview, visit: www.gov.uk/children-with-special-educational-needs.
The Key Stage 2 results used in this guide give the proportion of pupils achieving Level 4 (the level expected of most 11-year-olds) and Level 5 (above the level expected for most pupils). Throughout, 2013 data is used to rank schools - although it is important not to place too much weight on such rankings within a single city.
For GCSEs, data is more detailed: five or more good GCSEs = five or more GCSEs grades A*-C, including English and Mathematics; EBacc = English Baccalaureate - English, mathematics, a science, a language, and a humanities subject.
For A-levels, the reference in state profiles to high grades in "key" A-level subjects relates to subjects required by the Russell Group of 24 leading universities, including Oxford and Cambridge.
Inevitably, some of the information available may be either out of date or incorrect. Headteachers and chairs of governors change frequently; performance data takes a long time to be validated and published in a comprehensive and consistent manner; as a result, even official sources fail to keep up with all the changes.
This Brighton and Hove Independent guide is, we believe, the most detailed and definitive publication of its kind in any town or city in the country.
The usefulness of its contents, however, inevitably depends on a proper understanding - and a very personal interpretation - of the data.