Three studies examined high school and college students' proficiency with sourcing, contextualization, and corroboration skills when working with history documents. Findings indicated that students using "Sourcer's Apprentice"--a computer-based tutoring system to teach sourcing and corroboration--instead of regular classroom activities or a textbook-centered version of same content improved at sourcing, contextualizing, and corroborating on a transfer test and wrote better essays on the topic than the comparison group. (Author/KB)