This paper presents a script-based monitoring system for evaluating students' reasoning during problem-solving. Problem-solving processes are equipped with knowledge structures, which are named scripts. A script is a collection of slots for events and provides conceptual dependency between events. Therefore, Script-Based Monitoring Systems (SBMS) can issue assistance to students' requirements and explanations to incorrect activities immediately during problem-solving. The SBMS works as an assistant for circuit analysis. A solution script is designed for the problem-solving process of sinusoidal steady-state network problems by applying loop or branch current analysis. The script is broken up into three scenes: defining variables, deriving equations, and solving equations. After a problem is displayed to a student, she explains her own problem-solving process by sentences and equations. The purpose of the SBMS is to evaluate the student input and determine the control of the dialogue at every step. The evaluation of such events is done by the diagnostic module of the SBMS and the slots of the solution script are filled with the results. As a consequence, the SBMS can hold mixed-initiative dialogues with students. The SBMS is implemented in PROLOG.