The Public Accounts Committee published a report on widening participation in higher education last week, which highlights the big gap in university participation between young people from rich and poor backgrounds. The aim of the report is largely to question whether the £392 million of public money given to universities for widening participation over the past six years has been used wisely.

IFS' recent work on participation in higher education (HE) gives a strong indication of what sorts of spending might work and what won't. It shows plainly that outreach activities aimed primarily at A-level students cannot fix the problem - by the time poor children have reached 16, it's already too late for many. Their low attainment has already drastically reduced their chance of a university place.

Our research used newly linked administrative datasets following every state school student from one particular cohort through the school system, from age 11 to age 19, allowing us to observe the entire history of academic achievement and any resulting HE participation.

It found, for example, that only 12.7% of boys from the most deprived fifth of households attend HE at age 18 or 19, compared to 41.7% of boys from the most affluent fifth - a gap of 29 percentage points. The gap between the richest and poorest girls is even bigger, at 34.6 percentage points. However, we found that this 'socio-economic gap' in HE participation does not emerge at the point of entry into higher education. Instead it comes about because poorer pupils do not achieve as highly in secondary school as their more advantaged counterparts. In fact, the socio-economic gap that remains after controlling for prior attainment (that is, comparing individuals with similar records of academic achievement) is tiny, at just 1.0 percentage points for males and 2.1 percentage points for females.

The implication is that focusing policy interventions on disadvantaged pupils who are already in post-compulsory education is unlikely to have a serious impact on the socio-economic gap in HE participation. This is not to say that universities should not carry out outreach work to such students, but simply that it will not tackle the much larger problem, namely the underachievement of disadvantaged pupils in secondary school.