A group of 161 kindergarten and first grade children were instructed in mathematics using exercises in linear measurement to increase understanding of unit-quantity relations. A comparison group made up from two adjacent and comparable middle-class schools was taught mathematics without intervention into the mathematics content. Treatment and comparison groups did not differ in general conservation performance throughout the study. However, an ancillary study demonstrated that linear measurement competence is preliminary to linear conservation. After five or six months of treatment, the measurement group was vastly superior in measuring competence, but slightly inferior in typical first grade mathematics. Appendices include sample lessons and test items as well as data tables. (Author/SET)