Formative feedback plays an important role in assisting students in their learning process. However, administering information about student weaknesses and strengths is one of the challenges faced by teachers when implementing formative assessment. This study aims to develop a web-based formative feedback system that is able to provide specific feedback. This is a development research with steps including needs analysis, model design, model development, and limited model trial. The research has succeeded in developing a web-based formative feedback system through utilizing isomorphic multiple choice items, namely "Tryout" and "Webvoting" applications. The results of the initial trial, involving 22 high school physics teachers and 44 prospective physics teachers, showed that the model can be used by both students and teachers. The use of "Tryout" application allows the teachers to administer individual and groups of students' feedbacks. Based on the feedbacks and information, teacher also can discuss student's learning difficulties using "Webvoting" application. More extensive trials are needed to find out the effectiveness of this system.