The Cognitive Development Methods is a course that is quite difficult for students of the ECE study program at Universitas Terbuka who are required to be able to learn independently. Therefore, improvements are needed to learning materials to make it easier for students to achieve the expected competencies. The purpose of this research is to develop learning materials and cognitive development methods that are following the conditions and developments of the latest science. This development was carried out on a multi-year basis using the Borg & Gall model, and this study is the 9th step of the model, namely the formative test, which is using one-to-one evaluation with experts and users. The results of one-to-one evaluation generally state that the learning materials Cognitive Development Method is good in terms of the map of competence, the accuracy of technical concepts and terms of the field of science, the conformity of the material with the characteristics of Universitas Terbuka's students, clarity of summary, description of small tasks, and the accuracy of key test answers. However, this learning material still requires improvements in terms of accuracy of competency formulation, conformity of concepts and theories with standards for the course (ECE program standards in Indonesia), clarity of problem training, and lack of illustrations and images. So it can be concluded that this cognitive development method still requires further refinement before use.