England's schooling landscape is being remodelled and the move from hierarchical to heterarchical modes of governance has implications for systemic change strategies. Balancing local and networked autonomy with centralising policies complexifies choices for schools, creating tensions that this article explores through the context of curriculum resourcing policies. In particular, we consider the contemporary case of mathematics textbook schemes in England's heterarchical school system, comparing them with an earlier resource-driven systemic change programme--the National Numeracy Strategy--which was implemented in a more hierarchical governance system. Drawing on key ideas from implementation science and data from a Wellcome-funded study of primary teacher professional learning in mathematics in England, we exemplify the challenges of implementing centralised improvement policies in a nominally schools-led, self-improving, heterarchical education system. Each of the 19 participating schools had evolved a bespoke curriculum, and these hybridised 'mashups' of different resources were enacted with varying degrees of fidelity by teachers. We discuss the implications of this comparative case for systemic improvement, both in the use of educational resources and for policy implementation more generally.