Childhood obesity has increased to epidemic proportions during the past 20 years. The state of California mandates physical fitness assessment of all public school children in grades five, seven and nine, using the FITNESSGRAM/ACTIVITYGRAM battery. Data for 2005 show that for the body mass index (BMI) component, 33.6% of California fifth graders score above the Healthy Fitness Zone (HFZ), and this percentage remains constant from grades five to seven (33.6 to 33.3%) and seven to nine (33.3 to 33.1%). No California body composition data exists for children in kindergarten through fourth grade. In an effort to track the critical origins of childhood obesity, height and weight were measured to calculate the BMI for 554 children (304 males and 250 females) in grades K-3 from southern California. The purposes of this study were: 1) to quantify the percent of children above the BMI HFZ for grades kindergarten (K), one (1), two (2), and three (3), 2) to quantify the percent of children above the BMI HFZ at each grade level for gender, ethnicity (White and Hispanic) and socioeconomic status (subsidized and non-subsidized school meals; SES), and 3) to determine the greatest grade level change for gender, ethnicity and SES. Results showed that 3.3%, 7.5%, 12.2%, and 20.8% of children in grades K, 1, 2 and 3 respectively scored above the BMI HFZ. Results for gender, ethnicity, and SES demonstrated that the following percent of children scored above the BMI HFZ at each grade level, K, 1, 2, and 3, respectively: 1.4%, 9.9%, 17.5%, and 23.8% of males, 5.9%, 5.3%, 5.1%, and 16.9% of females, 0%, 2.3%, 10.7%, and 11.9% of Whites, 6.8%, 15.2%, 12.5%, and 38.6% of Hispanics, 5.3%, 14%, 18.5%, and 34.4% of children with subsidized meals, and 2.4%, 4.2%, 8.2%, and 11.4% of children with non-subsidized meals. Of the children classified above the BMI HFZ, the greatest grade level changes were as follows: grade (127.3% increase from K-1); gender (males 60% increase from K-1, females 231.4% increase from 2-3); ethnicity (Whites 365.2% increase from 1-2; Hispanic 208.8% increase from 2-3); and SES (subsidized 164.2% increase from K-1, non-subsidized 95.2% increase from 1-2). The current findings highlight the need to assess predictors of childhood obesity prior to the state mandated assessment in fifth grade. Additional discussion on significant grade level changes and their implications will be discussed.Keyword(s): early childhood, obesity issues, youth-at-risk