The main purpose of this study was to concurrently investigate Taiwanese high-school students' and their science teachers' conceptions of learning science (COLS) and conceptions of science assessment (COSA). A total of 1,048 Taiwanese high-school students and their 59 science teachers were invited to fill out two questionnaires assessing their COSA and COLS. The main results indicated that, first, although a handful of different patterns occurred, students and teachers were found to have similar COLS-COSA patterns. In general, students and teachers with COSA as reproducing knowledge and rehearsing tended to possess lower-level COLS, such as learning science as memorizing, testing, and calculating and practicing. In contrast, if students and teachers viewed science assessment as improving learning and problem-solving, they would be prone to regard science learning as increase of knowledge, applying, and understanding and seeing in a new way. However, the students' conceptions did not align with those of the teachers' in certain aspects. The students tended to regard science learning and assessment at a superficial level (COLS as "memorizing", "testing", and "calculating and practicing" and COSA as "reproducing knowledge"), while the teachers' conceptions were at a more sophisticated level (COLS as "application" and "understanding and seeing in a new way" and COSA as "improving learning"). It is evident that a dissonance exists between the students' and teachers' COLS and COSA. Based on the results, practical implications and suggestions for future research are discussed.