It’s a big question with many answers; often conflicting. I have been involved in education professionally for nearly 20 years, I am state educated but have had intimate ties with private education throughout that time.
The answer to the question is enormously affected by demographics. Most privately educated children will aspire (or at least their parents will) to A Levels, University and a career to follow. This will also be the case with many state educated pupils. However, (mainly) within the state sector there will also always be enormous quantities of students for whom school is just compulsory. They have to go and they look forward to leaving; often with few prospects and very little idea of what to do next.
It is these students that the system lets down the most.
If you leave school at 16 what should you know? Most people will agree that a basic knowledge of English and Maths (numeracy and literacy if you prefer) is a given – but what else?
In our heavily politicised system there is far too much emphasis on passing (so that the government can say what a good job they’re doing) and far too little on content.
To take one example it is possible for two students to both get an A* (A* being of course a nonsense concept in its own right) at GCSE without having done a single question in common. How can we possibly compare pier groups in this way? With multiple Examination Boards the statistics are meaningless. With this system there is also no standardisation of content excepting broad National Curriculum guidelines.
We need to sweep away the nonsense of the multiple exam board system, set up panels consisting of a mixture of academics and representatives from industry to decide exactly what people ought to know at 16 for each subject. There should be a single syllabus for each subject and everybody should sit the same examination.
Beyond 16 is the time to academically diversify, compulsory education should give everybody a solid grounding; even if they never read another word in their lives. Telling them they’ve ‘passed’ a meaningless exam helps nobody.