Across many academic disciplines visualisation and notation systems are used for modelling data and developing theory, but in child development visual models are not widely used; yet researchers and students of developmental difficulties may benefit from a visualisation and notation system which can clearly map developmental outcomes and trajectories, and convey hypothesised dynamic causal pathways. Such a system may help understanding of existing accounts and be a tool for developing new theories. We first present criteria that need to be met in order to provide fully nuanced visualisations of development, and discuss strengths and weaknesses of the visualisation system proposed by Morton. Secondly, we present a tool we have designed to give more precise accounts of development while also being accessible, intuitive and visually appealing. We have called this an Accessible Cause-Outcome Representation and Notation System (ACORNS). This system provides a framework for clear mapping and modelling of developmental sequences, illustrating more precisely how functions change over time, how factors interact with the environment, and the absolute and relative nature of causal outcomes. We provide a new template, a set of rules for the appropriate use of boxes and arrows, and a set of visually accessible indicators that can be used to show more precisely relative rates, degrees and variance of functioning over different capacities at different time points. We have designed ACORNS to give a precise and clear visualisation of how development unfolds; allowing the representation of less "static" and more transactional models of developmental difficulties. We hope ACORNS will help students, clinicians and theoreticians across disciplines to better represent nuances of debates, and be a seed for the development of new theory.