Writing is a complex process, and this complexity poses particular challenges when researchers and teachers approach the task of analysing young students' writing samples. This paper outlines a program of research undertaken to develop a writing analysis tool. The tool is designed to map shifts over time in the range of skills and competencies young writers use to communicate intended meanings and messages using standard writing conventions. Writing samples (N = 3193) were collected from 1799 students, in the two most populous states of Australia in 2010. The close analysis of 210 samples by four members of the research team supported the development of the tool. The tool and its application revealed key areas of learning and the current range of Year One students' writing in these areas. Presented in detail are two dimensions of children's writing as illustrative of the relevance and functionality of the tool to practice. This tool provides a research-based approach to the interpretation of students' learning about writing. While designed for the purpose of research, the tool also has the potential to help classroom teachers capture shifts in students' writing, assist teachers to provide feedback to students, and support teaching decisions.