An “inexpensive” trial policy improved all pupils’ literacy in the early years and had long-term effects on children who struggle with reading, a major new study has found.

The “teaching to teach” literacy study, which sent phonics consultants to support primary school teachers and tracked 270,000 primary school children from reception to year 6, showed persistent effects on non-native English speakers and pupils eligible for free school meals.

Study author Sandra McNally, Director of the Education and Skills Programme at the Centre for Economic Performance, said the “inequality-reducing impact” of the intervention alone justified the cost of implementation, which was “much lower” compared to other proven strategies such as reducing class size.

The trial, which involved 18 local authorities in England, employed one literacy consultant per ten schools to provide “synthetic phonics” coaching support for a year, mainly in reception and Year 1, but also in Year 2 and nursery.

Improvements in literacy were recorded in tests up to age seven for all pupils, but by the age of 11 there was no overall effect.

EAL and free school meals students still showed a positive effect of the intervention at age 11, however, which is “impressive”, said the authors, “given that the phonics approach is only actively taught up to the age of seven”.

McNally said: “It’s a key stage 1 policy and you’re still finding effects at key stage 2 that are quite big, for an important group of students.”

She also highlighted the low cost of the intervention and said: “Just the fact that it would help those disadvantaged pupils a lot, on its own probably justifies the cost of the policy.”

The authors also suggested that an early boost to literacy for pupils across the board could have additional benefits to learning, possibly in terms of allowing pupils to absorb other types of knowledge.

The researchers ended their paper by warning against the effects of academisation on local authorities’ ability to implement targeted teaching interventions.

The conclusion stated: “It is still unclear what roles local authorities may play in schooling, but it will certainly be massively diminished, and perhaps non-existent, once full academisation has happened. Thus the kind of policy we have studied in this paper will not be feasible once this has taken place.”

The Department for Education has been approached for comment.