Semiotic work is principled engagement in the making of meaning. The semiotic work of school-based learning entails interpretation and expression framed by the curriculum and the social practices of the classroom, and realized multimodally in diverse pedagogic interactions and activities. Micro-examination of the relationship between a teacher's multimodally constituted framing of a task and students' responses in drawing and writing on individual dry-wipe whiteboards investigates the resources they selected in order to demonstrate their engagement, to make their texts suited to how they would be used, and to represent in ways apt to the subject area. These fleeting texts were just one realization of meaning among others in the semiotic flow of the lesson. Notwithstanding the speed of production and erasing soon after, the students' investment of semiotic work was principled. Taking their efforts seriously provides the ground for supporting them as they learn to make texts apt to different discourses and genres. (Contains 2 figures.)