The Phonics Screening Check (PSC) was introduced in England in 2012 for Year 1 children (aged 5 and 6). There have been criticisms of the check in relation to its reliability and appropriateness as an assessment for early reading, although advocates of the check see it as a valuable tool in securing progress in early reading. This mixed methods study sought to evaluate the intended and possible unintended consequences of the PSC, foregrounding the voices of children and their teachers. This article reports on findings from the teachers' data. The study focused initially on questionnaire data from 14 schools (59 teachers) selected for their diversity in relation to attainment data (PSC and reading) and socio-economic status. Focus groups in seven of the schools (25 teachers) enabled a more in-depth exploration of teachers' views and practices in relation to the PSC. The study identified the 'negative backwash' of assessment. The PSC was seen as an end in itself, rather than a way of securing progress in one of the skills of reading. It found that, the assessment had become the curriculum, to the detriment of specific groups of learners (higher-attaining readers and children with English as an Additional Language). Teachers were found to use the assessment processes of the PSC as objectives for teaching rather than using them as the tools of assessment.