The agency has been commissioned by CLG to inspire people in places such as Manchester and Stoke on Trent to help foster talent in their communities.
Forster was awarded the contract following a competitive three-way pitch managed by the Central Office of Information (COI).
The news comes at a time when the 'Broken Britain' debate has become a major political hot potato. Last month, the Conservative Party claimed five million people have never worked under the current government.
Shadow home secretary Chris Grayling also claimed some inner city areas were so blighted by criminal gangs that they resembled The Wire, the cult US television series about crime in Baltimore.
Forster head of social marketing Ellen O'Donoghue said: 'Inspiring Communities is about investing in locally conceived, locally delivered projects that will get whole communities standing behind the talented young people in their midst and make sure communities play a bigger part in fostering and investing in that talent.'
She added that the aim was to 'break the cycle of generational underachievement by broadening young people's horizons and experiences'.
The focus is on 11- to 14-year-olds and the long-term target is to increase educational attainment, particularly to enable more young people to gain five A* to C GCSEs.
Fifteen projects will take place in deprived neighbourhoods targeting areas such as Barking and Dagenham, Cumbria, Manchester, Rotherham, Stoke on Trent, Barnsley, Kent and Bristol.
Each campaign will be led by a 'neighbourhood partnership' made up of representatives from local authorities, secondary schools, third sector organisations, local businesses and young people. The campaigns will each be awarded up to £450,000.
Forster and the 15 neighbourhood partnerships are considering activities based on Dragons' Den and The Apprentice TV programmes, while promoting positive local role models, community projects and 'outward-bound' activities.
The agency will work with the partnerships over the next two months to develop plans, which will then be implemented over the following two years.
HOW I SEE IT - ROSIE WINTERTON, LOCAL GOVERNMENT MINISTER
We need to allow talented youngsters, no matter where they live or what their parents do, to fulfil their potential. We recognise that young people from poorer communities can be less likely to aim high and can have low self-esteem, low aspirations and limited horizons that act as barriers to success.
This funding is about taking steps to redress that balance and goes to support those community-led projects that will best foster young people's talents. Funding will help young people broaden their horizons, grow in confidence and learn about opportunities that are available to them.