The purpose of this study was to present a class case that verified the validity, reliability, and usefulness of a portfolio assessment in a cohousing class in the housing area of home economics. To achieve this objective, 241 male and female students in eight classes of the third grade of a junior high school in Gyeonggi-do, Korea, were enrolled in a project class on establishing a cohousing village in which the portfolio assessment method was applied for a total of 10 sessions for approximately four weeks from May 24 to June 16, 2021. To ensure the validity of the portfolio assessment, we designed the lesson after presenting the curriculum goals in detail using the backward design model and developed a specific rubric and conducted all evaluations and feedback based on the rubric to ensure objectivity and reliability. The online tool Padlet was used as a portfolio, which allowed students to easily upload their work, receive feedback from the teacher, and interact with their peers. After the class, the students reflected on the rubric and were generally satisfied with the class using portfolio assessment. This study is expected to facilitate the use of the portfolio assessment method in the classroom, while also supporting student growth and development.