Educators are currently exploring the expanded use of a variety of new assessment tools in the classroom in response to pressures to enhance student learning. The present study examined quick writes as a tool in the context of third-grade classroom assessment. Third-grade teachers administered the same brief writing probe before and after students took a field trip to a wetlands. Analyses suggested that student responses did change to reflect learning gained on the trip. Post-trip responses were also related to an objective test covering the same content and to elements of the state standardized test. The measure was also sensitive to variations across classes that highlighted the need for stressing common administration guidelines (e.g., time allocation, nature and length of instructions) as a crucial element of classroom assessments re-administered across time. This study suggested that quick writes are a promising tool for classroom teachers that can be sensitive to instruction and potentially useful for instructional decision making. (Contains 4 tables and 3 figures.)