<p>This paper presents a systematic literature synthesis examining commercial curriculum resources and their effects on teachers’ workload, with a specific focus on lesson planning and preparation time. The review develops a typology spanning commercially published curriculum materials, including textbooks, scripted programs, online repositories, digital platforms, and more recently GenAI tools. Across resource types, the dominant policy and provider claim is that externally produced materials deliver a time dividend by reducing planning and preparation time. Our synthesis finds that evidence of sustained workload relief is limited and highly conditional. While some resources reduce ‘from scratch’ preparation, time is commonly shifted into hidden labour such as searching, quality-checking, curriculum alignment, contextualisation and accountability compliance. These dynamics also reshape teacher professionalism: highly prescriptive resources can narrow autonomy, while discretionary use can support adaptive curriculum-making. We conclude that new technologies, including GenAI, are likely to redistribute rather than diminish curriculum labour, intensifying the need to scrutinise efficiency claims alongside the workload generated.</p>