This article presents a large-scale evaluation study of over 3000 9-14-year-old students who participated in an engineering workshop during their school fieldtrips. Student perceptions right before and after, as well as two weeks after the workshop were captured and examined. Before the workshop, younger students and boys, generally exhibited higher interest, higher self-efficacy, and less negative stereotypes for engineering than their counterparts. Also, Caucasian students had higher self-efficacy and lower negative stereotypes than Hispanic students. Students' interest, self-efficacy, negative stereotype, and utility perceptions of engineering were significantly improved right after the workshop, and improved perceptions were maintained at the delayed-post (follow-up) survey. The results indicate that fieldtrips can significantly improve students' perceptions towards engineering and improved perceptions are not limited to the workshop day, but persist afterwards. The gender and ethnic differences in engineering perceptions in the youngest age group indicate that outreach interventions should begin in elementary school.