Recent years have witnessed a revival in the popularity of measuring need in developing and developed countries as a precursor to distributing health, education, housing, social security and social care resources. The concept of needs- led children's service has particular purchase in England and Wales, where there is a legal requirement for local authorities to identify and assist 'children in need'. Yet, children's services agencies have consistently struggled to do this meaningfully and efficiently. This article analyses the strengths and weaknesses of needs assessments in the field before discussing new methods that are appearing. The final section considers how to encourage children's services to shift resources into the new methods.