This paper reports on a study undertaken with the primary aim of investigating the role of wonder in the learning process. The study was carried out by a 9th grade science teacher in collaboration with a university professor. The teacher taught two classrooms of 27 and 30 students respectively, by trying to evoke a sense of wonder only in one of them. To this end the teacher identified ideas and phenomena as potential sources of wonder and initiated the instruction through these ideas and phenomena. Observation and especially student optional journals were the main instruments of the research. A quantitative analysis of journal entries made by the students of both classrooms, provided evidence for higher involvement for the students--both males and females--of the classroom where the teacher evoked a sense of wonder. Also an analysis of students' comments provided evidence that wonder, experienced as astonishment and a shock of awareness can help students change their outlook on natural phenomena. Moreover two paper-and-pencil tests administered at the end of the school year provided additional evidence that wonder had an effect on students' ability to remember "wonder-full" ideas and also an effect on better understanding, of at least, three phenomena. This empirical evidence of better retention and understanding is evidence of the role of wonder as an attention catcher and generally of the role of affective factors in the learning process.