The current education system is aimed at enabling students to deeply understand the knowledge provided, think critically, express their opinions openly and freely, and apply their knowledge in real life. Therefore, it is a modern requirement to use necessary and effective methods in the classroom that focus on developing students' thinking skills. This research was conducted within the framework of Lesson Study. The main goal of the study is to determine the effectiveness of the Hatsumon method in enhancing students' thinking abilities. The Hatsumon method is not just focused on receiving answers from students, but instead aims to develop students' thinking skills by asking quality questions, guiding students to clearly achieve the learning objectives of the lesson.

The effectiveness of the Hatsumon method have been studied in three classes (9C, 9B, 9N). Additionally, a research group consisting of three teachers was formed based on the Lesson Study approach. The lesson was conducted in the "Trigonometric Formulas" section. The relevance of the research lies in the fact that trigonometry topics are considered difficult for students. In many cases, students simply memorize the formulas without understanding their meaning and significance. This leads to shallow mathematical knowledge and causes difficulties in mastering subsequent topics. Therefore, it is essential to use methods that encourage students to think deeply, analyze, and prove their solutions. Various levels of questions were posed to the students. These questions helped students deeply understand the topic and find the correct solutions to problems.

During the research, nine students of different levels were selected for observation from each class. High-level students were able to immediately respond to the questions created based on the Hatsumon method and prove their solutions. Medium-level students, initially passive, became more engaged as the direction and content of the questions increased their interest, motivating them to express their opinions. Low-level students initially struggled, but with teacher support and well-posed questions, they gradually adapted to the questions posed to other students and began to take their first steps.

The method proved to be effective for students at all levels. At the end of the lesson, teachers and students wrote reflections and shared their thoughts. Students mentioned that not only had they gained a deep understanding of the knowledge, but also paid attention to the origin and meaning of the formulas. Teachers emphasized the importance of guiding students' thoughts through questions.

Based on the reflections and observation sheets conducted at the end of the lesson, the following conclusions were made:

• Students aimed to understand the meaning of mathematical concepts and prove them, rather than simply memorizing them.
• Activity in the lesson increased, as students felt they had the opportunity to express their own thoughts, rather than just providing the "correct answer."
• Group discussions, comparing multiple solutions, and listening to and analyzing the thoughts of other students were developed.
• Students noted that their thinking had changed by the end of the lesson and that searching for answers to certain questions was interesting.

In conclusion, this research demonstrated that the Hatsumon method develops students' deep thinking abilities, increases their interest in the subject, and improves their skills in justifying and expressing their thoughts. Through the observations and reflections gathered during the Lesson Study, an opportunity to improve teaching methodology in the classroom was created. It is recommended to continue using this approach in other topics of trigonometry and in other subjects, focusing on student development through teaching.

This study employs a mixed-methods research design to investigate the effectiveness of the Hatsumon method in developing students’ thinking abilities. The Hatsumon method, originating from Japanese lesson study, emphasizes the use of well-designed problem-posing questions to stimulate learners’ independent thinking, reasoning, and classroom dialogue. A mixed-methods approach is adopted to capture both measurable changes in students’ thinking abilities and in-depth insights into classroom processes. The study is conducted in a secondary school educational context, involving students exposed to lessons structured around the Hatsumon method over a defined instructional period. An intervention-based design is used, with an experimental group receiving instruction through Hatsumon-based questioning strategies and a comparison group experiencing conventional teacher-led instruction. Quantitative data are collected using pre- and post-assessment instruments designed to measure students’ thinking abilities, including analytical reasoning, problem-solving, and explanation skills. These assessments consist of open-ended and structured tasks aligned with curriculum objectives. In addition, rubric-based scoring frameworks are applied to evaluate the depth and quality of students’ responses, focusing on reasoning, justification, and conceptual understanding. Qualitative data are gathered through classroom observations, student work samples, and teacher reflective journals. Observation protocols are used to document the nature of teacher questioning, student engagement, and patterns of classroom discourse during Hatsumon-based lessons. Samples of students’ written and oral responses are analyzed to examine changes in reasoning strategies and cognitive engagement over time. Teacher reflective journals provide insights into instructional decision-making and perceived shifts in student thinking. To capture learners’ perspectives, student questionnaires or focus group interviews are administered, exploring students’ experiences of Hatsumon-based lessons and their perceptions of how questioning strategies influence their thinking processes. Quantitative data are analyzed using descriptive and inferential statistical methods to compare pre- and post-intervention outcomes. Qualitative data are analyzed thematically to identify recurring patterns related to cognitive engagement, reasoning development, and classroom interaction. Ethical considerations include informed consent, confidentiality, and voluntary participation.

The study is expected to demonstrate that the Hatsumon method effectively enhances students’ thinking abilities by fostering deeper cognitive engagement, reasoning, and problem-solving skills. By emphasizing carefully designed, open-ended questions, the method encourages learners to actively construct knowledge rather than passively receive information. One anticipated outcome is that students exposed to Hatsumon-based instruction will show measurable improvements in analytical reasoning, conceptual understanding, and the ability to justify their ideas compared to students receiving conventional teacher-led instruction. Pre- and post-assessments are expected to reveal gains in the quality, depth, and creativity of students’ responses. In addition, the study expects to show that the Hatsumon method promotes metacognitive awareness, as students reflect on their own thinking while responding to challenging questions. Classroom observations and student work samples are anticipated to reveal increased engagement in discussion, higher frequency of reasoning aloud, and more collaborative problem-solving among peers. Teacher reflective journals are expected to highlight the instructional value of Hatsumon questioning, including insights into lesson planning, scaffolding strategies, and the adaptation of questions to diverse student needs. Student feedback is anticipated to indicate that the method increases their confidence in reasoning and expressing ideas, fostering a more participatory classroom environment. Overall, the study is expected to provide evidence that Hatsumon is a practical and scalable approach for cultivating higher-order thinking skills in secondary education. The findings will contribute to research on lesson study, classroom questioning strategies, and cognitive development, offering practical implications for teachers aiming to implement thinking-focused instruction. Additionally, the research may identify potential challenges, such as the need for teacher training in effective question design and strategies to support all learners in responding thoughtfully.

Cajkler, W., Wood, P., Norton, J., & Pedder, D. (2014). Lesson study as a vehicle for collaborative teacher learning in a secondary school.Professional development in education,40(4), 511-529. Al-Ahdal, A. A. M. H., & Aljabr, F. S. (2023). The Role of Interlanguage Practices in Feedback Mechanisms: A Case Study with Saudi EFL Learners.World Journal of English Language,13(8), 638-638. Coenders, F., & Verhoef, N. (2019). Lesson Study: professional development (PD) for beginning and experienced teachers. Professional Development in Education, 45 (2), 217–230. https://books.google.kz/books?hl=en&lr=&id=PInAAwAAQBAJ&oi=fnd&pg=PA38&dq=structural+approach+grammar&ots=sYRhk7z2nJ&sig=IxzwRHR3rsk3GcPPXIK1UTbg9UY&redir_esc=y#v=onepage&q=structural%20approach%20grammar&f=false https://www.educationaldesigner.org/ed/volume3/issue11/article44/