Field trips are fun -- that's the first reason to take them.  Learning should be fun -- and face it, most people have to learn a few things if they want to pass the GED.
        People learn in many different ways.  Some people like to read to learn, others to hear, or to see, or to do.  But one thing is true for almost everyone:  the more different ways you learn something, the better you learn it and the more likely to are to remember it.  In other words, even if reading is the way you learn best, if you read AND see AND listen AND do, you will learn even better than if you only read.  And field trips, especially ones that involve students in engaging activities, provide lots of different ways to learn things that are important for the GED.
        Our trip to the Boott Cotton Mill  is a good example.  One of the most fun parts of the trip was when students worked on a simulated (pretend) assembly line printing "tea towels".  In reality, the towels would have been made of the cloth that was woven in the mill, but on our line they were made of paper. Students inked borders with markers, printed flowers with rubber stamps, cut the towels, and inspected the finished work.  Our tour guide put on a black hat to become an overseer who sped up the work until people had trouble doing it right.  Then he fired some workers and lowered the wages for those who remained because he claimed the mill owners needed to make more money.  All the mill workers then went to a meeting where they complained about their working conditions and made a list of demands to present to the owner, who granted a few of them.
        Believe it or not, this was an important economics lesson -- and economics is one of the subjects included in the GED Social Studies test.  Students didn't merely read about the relationships between owners wanting more profits, declining working conditions, and the rise of labor organizations -- they lived this lesson on the field trip.  It's now part of their experience, something they can draw on when they see questions like these on the social studies test.