Topics in introductory computer science courses involve diagrams. Every data structure (e.g., stack, list, tree, or graph) is best understood when the definition is accompanied by a diagram. Demonstrating control flow within a method, or parameter passing from one method to another, are more easily explained using circles, boxes, and arrows. This paper describes our experiences with a web-based tool called MessageGrid which facilitates interaction between instructor and students in the classroom. Focus is on the most recent MessageGrid feature: student submission using digital Ink. We provide examples of exercises we use and student responses. We summarize the results of a student survey evaluating this new technology. Finally, we draw conclusions and describe plans for the future.