A survey has shown that the most disadvantaged children loose up to 2 years. This has come to light, since pupils receiving free school meals usually sit GCSEs 2 years later than their peers. Although government promises to close the attainment gap on a regular basis, much still needs to be done. Furthermore, there is evidence for improvements but the difference between children from an economically disadvantaged background and their peers is still at 19.3 months at the end of 2016. There is a strong need for improvement at a faster rate since otherwise poorer children will valuable time in their education.
Source: http://www.bbc.com/news/education-40801167