This study compared the effects of teacher feedback and answers to the questions generated by students in a lecture-centered, large-sized class setting after considering the time the teacher spent providing feedback or answers. The following three research questions were addressed. (a) Are there any differences in the learning motivation level between students in the feedback and answer groups? (b) Are there any differences in cognitive engagement between students in the feedback and answer groups? (c) Are there any differences in achievement between students in the feedback and answer groups? The participants included 91 undergraduate students enrolled in a South Korean university. Feedback treatment and answer treatment were applied separately to two classes in the same undergraduate course titled “Structural Analysis I” for sixteen weeks of a semester. A survey and two achievement tests were conducted to assess the students’ learning motivation, cognitive engagement, and achievement. This study revealed the teacher feedback to be better or equally effective on learning compared to the teacher answering the student’s questions in a lecture-centered, large-sized class with more than 50 students after considering the teacher’s time-on-task. Teacher feedback to the students’ questions saves more time and is more critical than the teacher answering the students’ questions. These findings suggest a practical instructional strategy in terms of enhancing the learners’ cognitive engagement in large-sized engineering classes.