The doctoral advisor—typically the principal investigator (PI)—is often characterized as a singular or primary mentor who guides students using a cognitive apprenticeship model. Alternatively, the “cascading mentorship” model describes the members of lab- oratories or research groups receiving mentorship from more se- nior laboratory members and providing it to more junior members (i.e., PIs mentor postdocs, postdocs mentor senior graduate stu- dents, senior students mentor junior students, etc.). Here we show that PIs’ laboratory and mentoring activities do not significantly predict students’ skill development trajectories, but the engage- ment of postdocs and senior graduate students in laboratory in- teractions do. We found that the cascading mentorship model accounts best for doctoral student skill development in a longitu- dinal study of 336 PhD students in the United States. Specifically, when postdocs and senior doctoral students actively participate in laboratory discussions, junior PhD students are over 4 times as likely to have positive skill development trajectories. Thus, post- docs disproportionately enhance the doctoral training enterprise, despite typically having no formal mentorship role. These findings also illustrate both the importance and the feasibility of identify- ing evidence-based practices in graduate education.  Read more here.