This study estimates the causal effects of six corrective actions for children's problem behaviors, comparing four types of longitudinal analyses that correct for pre-existing differences in a cohort of 1,464 4- and 5-year-olds from Canadian National Longitudinal Survey of Children and Youth (NLSCY) data. Analyses of residualized gain scores found apparently detrimental effects of all corrective actions by parents and professionals on subsequent antisocial behavior and hyperactivity. In contrast, analyses of simple gain scores found only apparently beneficial effects. Temporally reversed analyses yielded the same pattern of results, consistent with selection biases and regression artifacts, not with unidirectional causal effects. The findings were similar for corrective actions by professionals (e.g., Ritalin, psychotherapy) and by parents (physical and nonphysical punishment, scolding/yelling, "hostile-ineffective" parenting). Longitudinal analyses should check for similar artifacts by implementing temporally-reversed analyses and by determining whether causally relevant coefficients would replicate without artifacts biased in their favor. (Contains 3 figures and 2 tables.)