Under England's Children and Families Act 2014, local authorities (LAs) have a statutory responsibility to provide an independent mediation service for cases of disagreement between parents or young people and the LAs where parents or the young person are considering an appeal to the First-tier Tribunal Special Educational Needs (SEN) and DisabilityWe examined the effectiveness and cost effectiveness of mediation in resolving such disagreements without recourse to an appeal to the Tribunal. Our data comprised three national surveys, two supplementary surveys and individual interviews with LA staff and parents to explore implementation of the new mediation system and the impact on appeals and costs over 2014-16 from 109 English LAs who provided data. Our findings indicate that families who took up mediation were significantly less likely to appeal to the Tribunal, absolute risk reduction 13.58% (95% CI: 10.20%, 16.97%). The cost saving across all cases, of different complexity, was £636,462 overall, approximately £500 per case. Overall, mediation was found to be a promising method of disagreement resolution, reducing appeals and producing savings in both financial and human well-being costs. To the best of our knowledge, this is the first study of both the effectiveness and cost effectiveness of mediation as a means of resolution of disputes about meeting children's SEN.