Very few research studies of the teaching of grammar and writing had been carried out with children younger than eight-years-old prior to the research reported in this paper. The research evaluated a new approach to teaching grammar and writing called Englicious. A Randomized Controlled Trial (RCT) and Implementation and Process Evaluation (IPE) research design, featuring 1,246 pupils aged six to seven-years-old in 70 primary school classes, was used to evaluate the effectiveness of Englicious for improving children’s writing. The approach was implemented in the context of the programs of study for grammar teaching in England’s national curriculum. The research found that there was no effect of the grammar teaching intervention on pupils’ narrative writing. The effect size for pupils’ sentence generation was sufficient to merit reflections about potential impacts of aspects of the intervention although this outcome also did not reach statistical significance. It is hypothesised that the manipulation of words, phrases and sentences, combined with practice at writing, may have contributed to any positive effect, although this would need to be confirmed in future research. It is concluded that until more research is done to investigate the effectiveness of different approaches to teaching grammar and writing with young children, existing evidence-based approaches are more likely to be effective to help young pupils’ narrative writing. England’s national curriculum specifications for teaching grammar and writing could usefully be reviewed to more closely reflect the evidence base from this field of writing research.