A study by Jenkins et al (2006) found that a £100 increase in per-student expenditure would produce a statistically significant increase of 0.05 grades in GCSE science (although the effects in English and Mathematics were not significant). In science, 1 standard deviation is equivalent to 1.77 grades, so that 0.05 grades is equivalent to a 0.028 standard deviation increase.

Since the average annual per-student expenditure is £2815, then this suggests that a 3.5% increase in expenditure secured an 0.028 increase in student achievement. This suggests that an increase of 35% in per-student expenditure would increase student achievement by 0.28 standard deviations. In other words, by increasing per-student expenditure by over a third, we could increase student achievement by roughly the same amount as was found in the KMOFAP formative assessment project (Wiliam et al., 2004).

Only the KMOFAP project did it at around one-tenth the cost.

References

Jenkins, A., Levacic, R., & Vignoles, A. (2006). Estimating the relationship between school resources and pupil attainment at GCSE (Vol. RR727). London, UK: Department for Education and Skills.

Wiliam, D., Lee, C., Harrison, C., & Black, P. J. (2004). Teachers developing assessment for learning: impact on student achievement. Assessment in Education: Principles Policy and Practice, 11(1), 49-65.