Working adult undergraduates can be broken into two groups: employees who study (those who work full-time and pursue postsecondary education to obtain skills necessary to advance in their careers) and students who work (those who work part-time and attend school full-time). In 1999-2000 roughly two-thirds of working undergraduates aged 24 or older reported that work was their primary activity, and among these nearly 70% combined full-time work with part-time attendance. These working adults make up a large percentage of the undergraduate population and nearly one-half received some sort of financial aid, including one-quarter who received aid from their employers. However, full-time work and part-time attendance combined with family responsibilities appeared to be barriers to completing a credential. Despite the fact that most employees who study thought it was important to earn a formal credential, 62% had not done so within 6 years. Moreover, among those who left, most did so in their first year. In contrast, their counterparts whose focus was on postsecondary enrollment students who work experienced more positive educational outcomes. These students, who were more likely to have fewer family responsibilities, were more likely to earn postsecondary credentials, especially bachelor's degrees. (Appendices include a glossary, technical notes and methodology, and supplementary tables. Contains 31 tables, 9 figures, and 16 references.) (MO)