Hi Ruth:
Field trips are dynamic learning experiences. Guest speakers have a great impact as well, but not as significant as the field trip.
I think the primary reason is students get a chance to actually see some aspect of the real work of work their being prepared for. This can transform a students effort, motivations, and imagination to a degree that many will begin to work harder and try to do their best because they visualize themselves in a potential successful career.
Regards, Barry