This paper presents an interactive mathematical tutor application to assist middle school students with solving single-variable linear and quadratic equations and two-variable systems of linear equations. The system uses a gestural, pen-based interface to mimic and enhance the traditional step-by-step method of solving algebraic problems on paper. After the student handwrites each step, the system detects any mistakes, highlights incorrect terms or wrong expressions, and provides specific, localized messages to help the student understand their errors. Two qualitative user studies were conducted at a local school to gather general feedback from some students and their math teacher. Results indicate that most students found the application easy to learn and fun to use. Real-time mistake detection and highlighting of incorrect terms informed students of their errors and improved their ability to solve similar problems. Although many students found the mistake detection and highlighting helpful, our studies also suggested that some students needed more active help. We are currently conducting a Wizard of Oz study to rapidly investigate enhancements to the user experience, which may address this limitation.