This paper presents a synthesis of research literature concerned with teachers' and school leaders' experiences of workload and work intensification. Forty papers met the inclusion criteria for the research synthesis. From the analysis, we drew out both definitional and experiential accounts. Firstly, while we mostly found a conflation of the concepts of workload and work intensification, there is a distinction between the two that was apparent in some studies. A clear explanation of how they are related is not evident across the suite of studies, although there have been recent attempts to quantitatively interrogate this issue. Secondly, the research indicates that the effects of workload and work intensification negatively impact teachers, in relation to health, wellbeing, and attrition. Further, teachers' capacity to deliver educational priorities which support the learning of all students is undermined by the experience of a heavy workload and heightened work intensification. The paper advances the notion of "time poverty" to explain how workload and work intensification function together in teachers' work. Without a clear understanding of the particular affordances and limitations of conceptualisations of workload and work intensification, interventions are unlikely to resolve the contemporary and damaging problem of time poverty for teachers.