The purpose of the study was to develop a valid and reliable tool for use in assessing motor skills in preschool children in field based settings. The development of the CHAMPS (Children's Activity and Movement in Preschool Study) Motor Skills Protocol (CMSP) included evidence of its reliability and validity for use in field-based environments as part of large epidemiological studies. Following pilot work, 297 children (3-5 years old) from 22 preschools were tested using the final version of the CMSP and the TGMD-2. Reliability of the CMSP and interobserver reliability were determined using intraclass correlation procedures (ICC; ANOVA). Concurrent validity was assessed using Pearson correlation coefficients to compare the CMSP to the original Test of Gross Motor Development (2(nd) Edition) (TGMD-2). Results indicated that test reliability, interobserver reliability and validity coefficients were all high, generally above R/r = 0.90. Significant age differences were found. Outcomes indicate that the CMSP is an appropriate tool for assessing motor development of 3-, 4-, and 5-year-old children in field-based settings that are consistent with large-scale trials.