The textbook is an essential source of knowledge, providing students with a wide range of necessary facts and action plans while serving as an important link between the creators of the curriculum and the teachers who implement it. Since textbooks are a mandatory teaching tool, they must be well designed to effectively promote student-centered learning activities. Properly selected and used textbooks can promote students' thinking and interest in science and help them understand complex scientific concepts.

The curriculum reform carried out in Republic of Croatia in 2019 brought significant changes to the biology curriculum, resulting in changes to the content and structure of biology textbooks. While the revision of the curriculum is desirable, without a comprehensive analysis of the results of these changes in schools, the reform cannot have its intended effect. One way of evaluating the effects of the implemented reform is to analyze the newly designed textbooks and their effectiveness for teaching. Studies on teachers' use of textbooks show that most teachers consider them the main source of information for lesson preparation. Teachers generally use textbooks as a guide for implementing the curriculum, and the quality of textbooks has a significant impact on the quality of their teaching. Although it is common practice for teachers and education professionals to be involved in the design and selection of textbooks, it is equally important to include the students' perspective in their development. Many researchers have noted that the student perspective is generally overlooked in educational research by teachers, schools and policy makers. However, many studies emphasize the importance of students as impartial critics of learning and teaching activities, whose opinions serve as a valuable source of data for improving the quality of education in schools.

The aim of this study was to investigate the attitudes of high school students and teachers towards biology textbooks in Croatia several years after the implementation of the reform. Data were collected from participants in various upper secondary schools across the country using an online questionnaire. Preliminary results show that the majority of students find the textbooks conducive to independent learning and easy to study, but opinions differ regarding the treatment of topics, coherence and logical sequence of content. Teachers have expressed dissatisfaction with the clarity and systematic nature of the textbooks, pointing to discrepancies in the alignment of content with the curriculum and different organizational structures among different textbook publishers. These results underline the importance of continuous improvement of biology textbooks based on specific contributions from both teachers and students.

Keywords: Biology textbooks, curriculum reform, education.