Objective: To analyze the anthropometric technique used by teachers on children from first grade, and to compare those measurements with those taken by a trained professional on the same children. Subjects and Method: Cross-sectional study in lst grade children from 19 municipalized schools and two subsidized particular schools from Vicuña County. An observation guide to register the fulfillment of the methodology recommended by the Chilean Ministry of Health was applied. Comparison of the results of the nutritional evaluation (BMI by age and height for age) according to the data of the teacher and the health professional was performed by the Kappa Index. Results: 426 were students studied, 90.6% of the universe. Only 27% of the teachers had received qualification and their methodology to weigh and to measure was inadequate in the majority of the cases. The Kappa Index was inferior to 0.8 and the more frequent errors of classification were underestimation of the low weight (1.9 vs. 3.3%), over-estimation of the overweight (21.1 vs. 18.1%) and obesity (23.0 vs. 20.2%). The agreement was smaller when the used technique was incorrect, in municipalized schools, in the rural area, or when the one in charge to measure was not teacher head (assistant teacher). Conclusions: The technique of anthropometric measurement was inadequate in most of the teachers, which determines errors in the nutritional classification. It is necessary more qualification and better instruments to obtain a more reliable data.