In the Iranian higher education system, including engineering education, effective implementation of cooperative learning is difficult because classrooms are usually crowded and the students never had a formal group working background in their previous education. In order to achieve the benefits of cooperative learning in this condition, this paper proposes a combination of cooperative learning and inquiry method. The method is implemented by grouping students in a way that the learning procedure is done in non-official class sessions by each group, while the inquiry method is done in the regular programmed class sessions. The study is performed in Islamic Azad University and the methods are implemented in two engineering economic classes with different numbers of students in each working group. The results are compared with a control class in which traditional teaching style is implemented. The results of analysis show simultaneous improvement of learning and behavioural attitudes of the students with cooperative learning plus inquiry method in the classroom with a fewer number of students in each working group.