The development of the National Languages and Literacy Institute of Australia (NLLIA) rating scales (bandscales) for English-as-a-Second Language (ESL) proficiency in school-age children is described, focusing on issues arising in the process. The origins of the larger ESL Development Project, of which the bandscales project was a part, are described and the program's principles are outlined. The bandscales project's objective was to create three rating scales for junior primary, middle/upper primary, and secondary school students to assist teachers in making instructional decisions and in monitoring and reporting progress. Three integrated strategies used in writing the scales are discussed: (1) adoption of a model of language ability able to account for the complexity of variables in the school context; (2) adoption of a three-tiered framework to account for the influences of age, experience, and context on students' second language development; and (3) incorporation of descriptions of second language ability in academic contexts. The process of validating the scales is also described, and issues related to implementation are addressed briefly. Contains 36 references. (MSE)