In this study, how fourth- to sixth-grade children perform measurement estimation was investigated. The data were collected by a measurement estimation task that contained linear and area estimations and interviews from 72 children, each in one fourth- (n = 21), fifth- (n = 32), or sixth-grade (n = 19) class at local public elementary schools in cities in north Taiwan. The results indicated significant differences in the performance of the children in the estimation task among the three grade levels. The sixth-graders were observed to outperform the fourth-graders but they performed similarly to the fifth-graders. Grade level also influenced children's ability to estimate area rather than linear estimation. The children's strategies used for estimating an object with a long length included Benchmark, Guessing, Looking, and Other strategies. [For the complete proceedings, see ED597799.]