This study compares learners' writing in an impromptu, timed writing (ITW) exam and in a process-based, timed writing (PBTW) exam to investigate the differences between these two types of assessments. A secondary objective of this study is to examine the test takers' attitudes towards the two exams. Forty participants taking ESL writing classes volunteered to participate. They had 45 minutes to write an ITW essay. Each also wrote a PBTW exam, with the order of the tests counterbalanced. For the PBTW exam, participants learned about the topic through videos, articles, and discussions; they planned their writing and wrote for 45 minutes. The participants finished by responding to a questionnaire about their attitudes toward the tests. The results revealed only a moderate correlation between the scores on the two exams (r = 0.417): Most participants scored higher on the PBTW exam. The participants wrote significantly longer essays and used more verb phrases per T-unit on the PBTW exam. Sixty-two percent of the participants thought that the PBTW exam was easier for a variety of reasons--they received background information about the topic before they wrote, they discussed their ideas in groups, and they had time to plan their essays. Limitations of the study and implications for ESL programs and construct validity issues are discussed.