Cities in England with high youth unemployment must do more to raise young people's attainment in maths and English, a report says.
Research by Centre for Cities found a strong link between results in English and maths and youth joblessness.
It found that between 2007 and 2010, an average of almost 50% of pupils in cities left education without GCSEs grade A* to C in maths and English.
The think-tank says the situation leaves youngsters unable to get a job.
The report cites towns and cities such as Hastings and Grimsby, where the youth unemployment rate between 2007 and 2010 was 8.4% and 8.8% respectively.
The percentage of youngsters getting the official government benchmark of five A*-C GCSEs, including English and maths, in these areas was 35% and 45% respectively.
However, in Cambridge, where youth unemployment stood at 1.3% for the same period, the percentage of young people getting five good GCSEs including maths and English was 54%, the report says.
The findings show that in 1996-97, schools in cities with more buoyant economies - such as Cambridge, Oxford and Reading - had the largest numbers of pupils gaining at least five C grades at GCSE in any subject, while struggling cities, such as Middlesbrough and Hull, had the lowest.
By 2009-10 this gap had disappeared.
But a gap remained in the numbers of pupils gaining the benchmark of five A*-C GCSEs including English and maths.
The report raises concerns that over the last few years, schools have been encouraging pupils to study for qualifications that are seen as easier to achieve to boost their position in league tables.
It concludes: "Incentives in the education system mean that pupils in struggling cities in particular are not being equipped with the skills required in the changing labour market.
"This is likely to reduce the employment opportunities of these people and compound the skills issues that these cities face."
A government source said: "Under Labour millions of children were pushed into non-academic qualifications that were of little value.
"The government is raising standards by allowing only the best qualifications to count in the league tables and increasing the number of children doing the academic subjects that businesses, parents and universities value most."
The chief executive of Centre for Cities, Joanna Averley, said: "We know that schools in some areas have a really difficult task, but the system must incentivise schools to support pupils to get good qualifications in maths and English.
"The government has taken steps to address this issue, but they could go further.
"This rebalancing is needed urgently to ensure schools are equipping young people with the basic numeracy and literacy skills they will need to get a job."
Figures released by the Office for National Statistics in October showed the UK jobless total for 16- to 24-year-olds hit a record high of 991,000 between June and August 2011.