Schools need to make strategic decisions regarding the practicalities of delivering interventions for students struggling with foundational literacy and numeracy skills. This includes planning -- or designing -- how the overall learning environment and experience of the intervention will work to obtain desired results, not just the instructional content it will consist of. This research report uses evidence to provide guidance for secondary school leaders making decisions about staffing, timetabling and intensity when delivering interventions in schools. It focuses on 3 key design considerations that influence the effectiveness of an intervention program: (1) intensity -- group size, frequency, length and duration of interventions; (2) timetabling -- how schools make time for tiered interventions in their regular timetable; and (3) staffing -- how schools develop a staffing structure that can support the delivery of intervention instruction.