The paper reports on aspects of an ESRC project, "The impact of Performance 'Threshold Assessment' on teachers' work" (ESRC R000239286). The paper begins by explaining the nature and technology of "Threshold Assessment," and its location nationally within the performance management system recently introduced into schools in England. We review the monitoring procedures adopted for Round 1 of "Threshold" and draw attention to the limitations of such statistical data as are available. We locate "Threshold" within recent international developments characterised by managerialism and the culture of performativity that have increasingly come to dominate both the nature of policy-making and definitions of 'professionalism'. Drawing on interview material gained from thirteen case studies carried out in primary and secondary schools and in Local Education Authorities, we analyse the ways in which "Threshold Assessment" carries different significance for women and men teachers, heads and threshold assessors. We conclude that the new policies represent a further step towards the masculinization of education.