We report a new phase of research of the scaling of Cornerstone Maths (CM), technology-enhanced curriculum units for lower secondary mathematics that embed dynamic mathematical technology (DMT). These combine web-based DMT, pupil and teacher materials, and teacher professional development that focus on developing the mathematical knowledge and pedagogies for teaching with technology. This paper presents the background research with teachers using CM (111 teachers from 42 London secondary schools in the period 2014-2017) that suggests the need for a web-based "professional development toolkit" to support the sustainability of the innovation and "within-school" scaling beyond the timeline of the funded project. It concludes with the research basis of the toolkit's design principles and structure that are designed to support teachers to implement DMT in their classrooms.