Deployment and impact of support staff (DISS) project
The results were striking: 16 of the 21 results were in a negative direction and there were no positive effects of TA support for any subject or for any year group. Effects across the years were roughly equivalent to 1.5 National Curriculum sub-levels for English, 1 sub-level for Maths, and about half a sub-level for Science. Those pupils receiving the most support from TAs made less progress than similar pupils who received little or no support from TAs. There was also evidence that the negative impact was most marked for pupils with the highest levels of SEN, who typically receive the most TA support.
The extensive data for this large scale study was used to examine effects of class size on pupil behaviour and teaching through primary and secondary school stages
Blatchford, P., Russell, A. and Webster, R. (2012) Reassessing the impact of teaching assistants: How research challenges practice and policy, Oxon: Routledge http://www.amazon.co.uk/Reassessing-Impact-Teaching-Assistants-Challenges/dp/0415687640
The Deployment and Impact of Support Staff (DISS) study is the largest study to date of the deployment and impact of support staff in schools. It was conducted between 2003 and 2009 in UK schools. The analysis studied the effects of the amount of TA support - based on teacher estimates of TA support and systematic observations - on 8,200 pupils’ academic progress in English, mathematics and science. Two cohorts of pupils in seven age groups in mainstream schools were tracked over one year each. Other factors known to affect progress (and the allocation of TA support) were taken into account in the analysis, including pupils’ SEN status, prior attainment, eligibility for free school meals, English as additional language and deprivation.
Here is a 2016 lecture on the DISS project given by Peter Blactchford at the University of Melbourne - the first of their Dean's public lecture series.