Abstract: AlgoSketch is a pen-based system for entering and editing mathematics. It supports interactive computation and early-stage mathematical algorithm design. In its paper-like environment, mathematical expressions can be en- tered anywhere on the page. Recognition and computational feedback are given in real time. We present results of a formative user evaluation of AlgoSketch, examining its applicability as a new interaction paradigm and users' overall experience with its mathematical entry, feedback, and computational support. Using a goal, question met- ric (GQM) framework, we evaluated AlgoSketch using efficiency, effectiveness, and satisfaction metrics. Logging data was supported by a post-questionnaire and anecdotal data. Results indicate acceptance of the AlgoSketch paradigm; strong potential for workplace utility, and a need for better mathematical expression recognition.