The piecewise latent growth models (PWLGMs) can be used to study changes in the growth trajectory of an outcome due to an event or condition, such as exposure to an intervention. When there are multiple outcomes of interest, a researcher may choose to fit a series of PWLGMs or a single parallel-process PWLGM. A comparison of these models is provided with an illustrative example using data from the Early Childhood Longitudinal Study, Kindergarten Class of 2010-11 (ECLS-K:2011), and a Monte Carlo simulation study. Conditions manipulated included sample size, location of the transition point, the number of time points, and covariate effect size. The results showed that the power to test parameter estimates with both models depended on the two-way interaction of sample size and covariate effect, and the three-way interaction of sample size by the number of time points by transition point location. Parameter coverage also depended on the three-way interaction of sample size by the number of time points by the transition point location. Recommendations for the use of the PWLGM are provided.