This design-based research study is aimed at two goals: (1) developing a feasible case-based instructional model that could enhance college students' ill-structured problem solving abilities, while (2) implementing the model to improve teacher education students' real-world problem solving abilities to deal with dilemmas faced by practicing teachers in elementary classrooms. To achieve these goals, an online case-based learning environment for classroom management problem solving (CBL-CMPS) was developed based on Jonassen's (in: Reigeluth (ed.) "Instructional-Design Theories and Models: A New Paradigm of Instructional Theory, 1999") constructivist learning environment model and the general process of ill-structured problem solving (1997). Two successive studies, in which the effectiveness of the CBL-CMPS was tested while the CBL-CMPS was revised, showed that the individual components of the CBL-CMPS promoted ill-structured problem solving abilities respectively, and that the CBL-CMPS as a whole learning environment was effective to a degree for the transfer of learning in ill-structured problem solving. The potential, challenge, and implications of the CBL-CMPS are discussed.