“Six applicants for every place”, “heavily oversubscribed”: these sorts of claims are often used to establish how popular - and, by implication, how successful - schools and colleges are. But they should be taken with a large pinch of salt.

Being able to measure demand is important in a market system. Saying “we are oversubscribed” is a neat, shorthand way of letting punters know the scarcity value of the commodity you are offering; that more people want it than can get it.

But choosing a college is not generally a single-outcome decision. The post-16 free-for-all allows consumers to make multiple applications. However, they will ultimately choose only one institution, so a high number of applications is an inadequate measure of demand. What matters is the conversion rate - the proportion of applicants who actually enrol.

Our college has always had more applicants than places and has therefore always been “oversubscribed”. This is not because we are selective but because we understand that many students make multiple applications. In a competitive environment with new post-16 providers opening up every year, this will intensify.

Selective post-16 providers have no problem turning people away as they think it contributes to an impression of success. Comprehensive post-16 providers operating in a market have to understand the dynamic of that market if they want to fill their places without rejecting students.

This is quite a challenge, and is part of the process of dealing with the marketisation of our sector.

“Choice and diversity” was the previous government’s euphemism for this policy, putting a positive spin on something that was not particularly popular with public-service users. In education, it meant promoting new providers and encouraging competition between them. Looking back to those pre-2010 days, this seems pretty tame, but it paved the way for the current government’s market strategy for education.

The idea is that good schools will attract more students and less good ones will be motivated to improve by the competition. The less popular schools might get some support to get better, or be rebranded and relaunched with new leadership. The possibility of decline, failure or closure sharpens everyone’s focus.

And we like choice, don’t we? When we’re shopping we like to be able to choose between different products, check prices and value for money and make our own judgement about what’s best for us. Choice is a good thing - up to a point.

But do we really want to shop around between different educational offerings for ourselves or our children? Can education be both a public service and a commodity? Isn’t it too important to be placed in the hands of competing providers based on what they are prepared to offer within the local market? We’re paying for it anyway, so surely we want the best possible public education as a civic right.

As with our other public services, we want education to respond to our needs and aspirations and, ultimately, to be accountable to all of us. Within a system of public education, any choice about what is available - any specialist programmes or facilities, any experimental or innovative approaches - should be open to everyone and not the result of luck.

When a market is combined with the lack of a coherent national framework, the result is actually a loss of choice. In post-16 education, for example, providers need to be of a certain size to offer a full range of courses including minority subjects such as A-level German or Classical civilisation. By encouraging new, smaller, competing providers that cannot support niche subjects, you give the impression of greater choice, but in fact students end up having fewer courses to select from.

So we should be very cautious about the panacea of more choice and diversity in education - we could find ourselves losing more than we gain.

`War of all against all’

Another problem is that an ideal market requires well-informed consumers who are in a position to decide between products based on accurate information about the things that matter to them, such as quality and price. How much more important is this in the case of education, which has longer-term consequences than most purchases?

This, therefore, means that consumers - whether students or their parents - must have access to good information, advice and guidance from disinterested experts. It means trusting and understanding the value and limitation of the data in league tables. It also means being able to evaluate a wide range of other “objective” published data and statistical claims.

In reality, the post-16 market is far from perfect. Providers with good reputations will tend to attract the kinds of students who are most likely to further enhance their attractiveness in an upward spiral of positive feedback. Other institutions can easily fall into a downward spiral.

It is widely known that many secondary schools with sixth forms work hard to ensure that their most promising students “stay on” at 16. This falls far short of the ideal of providing independent advice about the full range of options and is a natural product of the market system with all its various incentives and pressures.

On top of this, markets lead to marketing. Glossy brochures, prospectuses, press releases and advertising campaigns boosted via social media are now key elements of many providers’ strategies. They aim to amplify recruitment and manage reputation and are seen as essential for survival.

At the moment it seems that in the Hobbesian “war of all against all”, where every education provider is clamouring for attention in the marketplace, there is no way of stopping us all from spending public money on campaigns that portray us in the best light. Let’s just hope that we all have enough integrity to ensure the stories we tell are reasonably accurate and that our consumers aren’t too disappointed when they have a chance to test the reality against the rhetoric.

Eddie Playfair is principal of Newham Sixth Form College (NewVIc) in East London. Follow him on Twitter at @eddieplayfair