Although professional counselors have distinguished themselves among helping professionals through a focus and foundational framework in normal human growth and development over the life-span, a majority of programs neglect to incorporate training opportunities enabling students to translate developmental theory to clinical practice. In this mixed-method study, the researcher explored the effects of a human developmental counseling application curriculum and examined cognitive complexity levels among counselor trainees. Qualitative results support gains in both the integration and application of developmental content while quantitative results offer partial support for cognitive complexity gains among trainees. This study identifies a curricular training experience in which counselor trainees' integration and application human developmental theory as well as cognitive complexity, are notably enhanced.