The Transtheoretical Model (TTM) has been extensively validated in representative samples of adult smokers. Stage effects, i.e., the patterned relationships between Stage of Change (SOC) and other TTM variables, have been reported in a variety of samples. This study describes reliability data for the TTM variables and tests the stage effects with an ethnically diverse sample of 296 parents with young children. On the basis of theory and previous empirical evidence from a general population, it is possible to make quantitative predications about the magnitude of the expected effect sizes for the Decisional Balance, Situational Temptations, and Processes of Change subscales. For each variable, both a test of significance and a comparison with the expected effect sizes is reported. Results indicated significant stage differences for 8 of the 11 TTM subscales, and all quantitative predictions were confirmed. This study supports the use of TTM measures in an ethnically diverse sample.