In recent years, observational practices have been adopted in teacher training courses to improve practical skills of intending teachers. We investigated how intending teachers acquired instructional skills through observational practice. In order to evaluate improvements in instructional skills of intending teachers, we asked them to develop selflearning materials in science for junior high schools, before and after an observational practice. We assessed changes in the quality of self-learning materials developed in the two conditions. Results indicated that the overall evaluation of the self-learning materials changed to positive after the observational practice. In addition, after the practice, the intending teachers explained the figures in the self-learning materials, and developed selflearning materials with a hierarchical appearance. These improvements in developing the self-learning materials may have resulted from the consideration given to the student and the class perspective. These considerations may have given them incentives to improve the students' comprehension. It is concluded that observational practice was effective in developing instructional skills.