Teacher and teacher trainees have been introduced to practice Thailand Lesson Study incorporated Open Approach Model as the problem-solving-based teaching approach for the past two decades. The problem-solving-based teaching approach has to begin with posing open-ended problem situation in order to encourage students to solve the problem independently using their own method. Therefore, open-ended problem situation design is considered a key factor for teachers or teacher trainees to provide sufficient opportunities to students’ learning experiences in solving the problems (Inprasitha, 2017). As a result, this research was aimed to use video recordings of classroom teaching and experts’ reflection practice to analyze teacher trainees’ abilities in designing open-ended problem situations. A total of 10 teacher trainees were selected from the Department of Mathematics (English Program), Faculty of Education, Valaya Alongkorn Rajabhat University under the Royal Patronage using a purposive sampling technique. A multi-cases study survey research design was employed using a qualitative approach. There were four research instruments used, namely lesson plan, video and audio recording, field notes, and interview protocol. Data were collected using various sources such as research lesson plans, audio, and video recording as well as interviewing. The results revealed that teacher trainees utilized classroom teaching videos to support them in clarifying indecisive problem situations, revising the sequence of teaching, and modifying appropriate words used in giving the direction of the problem situations. On the other hand, the experts’ reflection video has successfully assisted them to have a better understanding of mathematical contents in problem-solving teaching approach and teacher trainees’ intention of each action in the learning activities.

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