In a speech to CentreForum on Wednesday, the Deputy Prime Minister Nick Clegg declared the government’s commitment to promoting a fairer society. For him this means focusing on intergenerational mobility – in other words, reducing the extent to which a person’s income and social class are determined by their parents’ fortunes.

The Deputy Prime Minister identified a number of key barriers to social mobility including inequalities in education, the gap between further and higher education, early-years inequalities, the level of parental involvement and the difficulty those from disadvantaged backgrounds have entering some professions. The overarching theme, as emphasised by the Chancellor George Osborne, is improving equality of opportunity with a particular focus on education at all levels.

While noting that improving social mobility is a long term goal, Clegg’s speech suggests that he does not grasp quite how long the timescale is for measuring genuine change here. Governments are rarely in power long enough to see the impact of initiatives in this area – even those administrations that serve for 2 or 3 terms. It is no coincidence that the most influential research on social mobility has been based on longitudinal surveys that were started in 1958 and 1970: timescales of 30 years not 30 months.

In the coming months the Resolution Foundation will publish a report on the issue of intra-generational social mobility in the UK. Our work highlights the extent to which those on lower incomes can expect remain on low incomes throughout their working lives. This research takes account of trends in intergenerational mobility but also shows that economic opportunity and the chance to progress through work is becoming a more distant hope for those at the bottom of the income distribution.

Our analysis of the NCDS shows that people have found it increasingly difficult to improve their position in the income distribution. In part this is due to unequal income growth that has disproportionately benefited those at the top. The chart below shows that between 1981 and 2008, median income in the survey’s cohort grew by 386 percent, but in the top decile income grew by 1009 percent. In other words, the rungs of the income distribution ladder have grown further apart over the last 30 years.

Chart 1: Change in gross weekly earned income by decile, 1981-2008
Source: National Child Development Study, sweeps 4 and 8

That the rungs of the ladder have grown further apart is not only bad news for inequality, but also for mobility. The step required for people to move out of their income group is larger than ever, and fewer people are moving out of their income group over the course of their life.

Further NCDS data shows that by and large, a person’s income group is decided by age 32 and that those classified as “higher earners” (defined as deciles 9 and 10 in the distribution) are the least likely to experience a change in income group. People also become less likely to change income group as they get older which suggests that people are becoming “stuck” in the income distribution with little hope of progressing.

So what does this mean for the coalition’s commitment to social mobility? Nick Clegg may be right to focus on education although without other assets – social and financial – it won’t be sufficient. Our research highlights the importance of considering mobility and economic opportunity within generations as well as between them. The Deputy Prime Minister and his new colleagues also need to understand more about how to help people progress during their working lives. As the state retirement age goes up, these working lives will grow longer and this question will become more pressing.

Those currently in or approaching employment need to be assured that there will be opportunities for them to progress, and not just in their early career but throughout their working lives. A commitment to increasing the number “good jobs”, a more equitable geographical distribution of those jobs, fair pay, and investment in continual workforce training and development are all needed to ensure that intra-generational social mobility does not stagnate.