In addition to assessing the rate of change in outcome measures, it may be useful to test the significance of outcome changes during specific time periods within an entire observation period under study. While discussing the delta method and bootstrapping, this study demonstrates how to use these 2 methods to estimate the standard errors of the predicted mean changes in the outcome of interest. Different latent growth models were run, and the results of the delta method and bootstrapping were compared. The findings of the study suggest that the 2 methods, bootstrapping in particular, may be very useful to those who are interested in scrutiny of outcome changes in longitudinal studies.