This paper investigates the effects of time constraints on writing performance of Korean college students by comparing the overall quality of two types of writing samples-the term paper with a 5-week time allowance and the in-class timed essay with 30-minute time constraints. Thirty-nine college students majoring in Englishlanguage education participated in the study, and their compositions were compared in terms of 5 criteria. To ensure the compatibility of the two different types of tasks, two textbook passages whose topic was similar to each other were presented to the students. The writing task in both conditions was to build a lesson plan in an essay format explicitly detailing the rationale for each activity. The t-test results suggest a meaningful difference in the areas of content, language use, and mechanics; but not in organization and vocabulary. The results indicate that there are limitations on measuring students’ writing ability under timed conditions, which was also validated by survey responses collected at the end of the experiment. Implications for writing assessment are offered.