Despite efforts to make school science appealing, students' negative attitude toward it persists globally. This qualitative study elucidates how and why undergraduate students in Japan had declining attitudes toward school science during primary and secondary school. Twenty-two first- and second-year students at a Japanese national university participated in small focus group discussions. Data sources were the participants' focus group data and written accounts on factors that influenced their attitudes toward school science. The grounded theory approach was applied to code the data, which resulted in 42 codes under 11 domains. As the analysis progressed from lower to higher grades, the domains diversified and the frequency of codes increased. The resulting hypothetical model comprising 10 code domains reveals the complex interrelationships that cause attitudinal decline toward school science. 'Understanding' is positioned at the centre of the model, thus indicating the importance of cognitive aspects when considering this affective issue. The findings indicate that the development of two teaching methods is urgent: a mathematics-centric approach and innovative hands-on learning.