In one of the scenes in the GLEF video segment Journey North: Children Practice Real Science, the teacher tells her students they are "going to follow the path of the monarchs." She is standing next to a television when she says this, and there is a small piece of white card stock with some numbers on it taped to the right of the screen. The numbers represent latitude and longitude, and though she does not mention it, one can assume it is the location of their school.

Latitude and longitude are highly conceptual in nature, only appearing concretely on maps and perhaps at specific places along the equator where a community has decided their proximity to the demarcation is worth celebrating. Many teachers find it an extremely difficult topic to teach, and most adults, if they dare to be honest, have to admit it is a concept they do not have mastery over.

Many times I ask a room full of educators something along the lines of, "If I am in the southern hemisphere, and moving in such a way that my latitude is decreasing and my longitude is remaining constant, which direction am I headed?" One or two bold answers, often correct, may be offered, but the vast majority remains silent and looks around a tad sheepishly. They really don't know. (The answer is at the end of the column.)

But there is a technological tool that allows anyone to come to truly understand latitude and longitude and in that way learn to make use of it. We see this tool being most effectively used in the video segment Toad Tracking: Science and More through NatureMapping, in which students collect data on the habitat and habits of horny toads in western Washington state. The device is a global positioning system (GPS) receiver, a handheld device that utilizes an ability to communicate with geosynchronous satellites (those that stay in one place in space relative to Earth) to geometrically determine its location on the planet.

Because of the receiver's unique ability to make latitude and longitude real, every school should have one. Below are some tips to help you better understand these devices and be smarter about selecting a device to use with your students.

You Have to See It Work

It is difficult to understand just how a GPS unit works until you hold one on your hand and see it do its thing. It therefore makes sense, if you are unfamiliar with the technology, to seek out GPS users in your community and ask them to show you the ropes. Hunters, fishermen, boaters, surveyors, members of the military, hikers, pilots, farmers, and geocachers are all people outside academia you will find making purposeful field-based use of this tool. Talk to your neighbors and find someone who uses a GPS, and ask them to do a couple things: First, give you a tutorial, and then allow you to take it for a spin on your own. And, as you use it, think about latitude, longitude, and your students.

Get One with Maps Built In

Some of the least expensive GPS receivers do not include maps. They can give you your latitude and longitude, but they lack the ability to put you on the map. Choose a GPS that includes maps so that your students can not only get the coordinates of their location but will also get a bird's-eye view of where they are. Also, because these maps zoom in and out, you can use them to help your students get a better understanding of where they are in reference to the rest of their neighborhood, town, state, region, or even country.

But Can GPS Receivers Handle the Kids?

Many receivers are specifically designed to be mounted in cars, boats, or airplanes. Because you need a handheld model, however, it is especially important that you speak with people who spend time in the woods, on the ground and roughing it, in order to be sure you choose a model that will stand up to the rigors of student fieldwork.

For instance, some GPS receivers are specifically warranted to be waterproof for a certain amount of time -- say, five minutes -- in order to convince outdoors folks they can handle the occasional dunking that can happen during camping or hiking trips. You'll no doubt agree this is a valuable feature to have in place when heading into the field with middle school or high school biology students. Just because it is high tech does not mean it has to be fragile.

More Than Just Latitude and Longitude

The ability to provide latitude and longitude is the core utility of a GPS receiver, but software applications enable many other functions. For instance, marking waypoints, or locations, allows you to remember where you were and to name the locations so as to inform you of what was there. Users can also make the receiver calculate point-to-point distances between waypoints and, on some receivers, calculate the area of a space the user has circumnavigated.

p>Many, if not all, GPS devices are also capable of calculating elevation, or height above sea level -- another important factor when collecting scientific observations. Suffice it to say, software capabilities need to be part of your calculation when deciding on a GPS receiver that will become part of your teacher's toolbox.

Answer to the question of latitude and longitude at the beginning of this entry: Latitude decreases as one approaches the equator, and, because I was in the southern hemisphere to begin with, I had to be headed north.

Moderator's Note: Look for Part 2 of Jim's series on GPS technology in the classroom coming on Wednesday.