Much research on early measurement learning is small-scale and dependent on the items used. While such research is helpful for indicating the key aspects of learning length, it does not give teachers a clear indication of the expectations for student learning of them. This paper presents substantial data from a large project that used individual interviews to assess student learning against "growth points" or key stages in children's learning, over a range of domains including length. Data from interviews conducted twice a year with more than 1000 children in each of the first three years of school are used to indicate appropriate targets for student achievement. Basically it is suggested that the key targets for the learning of length in the first three years of school are, respectively, learning to compare, learning to use a unit iteratively, and measuring using formal units. (Contains 4 tables.)