I run the extern program at my hospital and here are a few of my thoughts -- based on my knowledge of programs in general -- with no knowledge of the specific programs in your geographic area.
There seem to be 3 basic kinds of extern programs. The first kind is simply a slight upgrade from a nursing assistant position designed mainly as a part time job for nursing students. There may be a few extra classes and some additional flexibility in scheduling, but the work functions are pretty much the same as a nursing assistant, but with perhaps a few more "advanced" tasks included. These programs generally run throughout the year on an ongoing basis. Some are wonderful learning experiences: others are just a way for the hospital to get some inexpensive laborors and the students to get some cash while becoming more comfortable in a hospital setting
The second type is designed more as an educational program for the students. The externs are paired with preceptors and work closely with those preceptors performing job functions that nursing assistance usually don't get to do -- such as giving medications, working with central lines, etc. The emphasis is on socializing the extern to the RN role and not on having the extern substitute for a nursing assistant. Such programs may offer more classes as well as other paid learning experiences, such as opportunities to shadow nurses on other units, etc. Because the externs are not included in the staffing count that day, externs are free to observe/help with interesting procedures, accompany patients going for tests or surgery, etc. Most of these programs are primarily designed as summer programs for students in-beteen the junior and senior year of nursing school and may require a full-time committment for the summer.
Some programs are hybrids -- they focus on the education in the beginning (during the summer), then allow the externs to stay throughout the winter on a part time basis in a role more like a nursing assistant. (The program I run is such a hybrid.)
So ... all you students out there hearing and thinking about externships ... be sure you know what kind of program you are applying for. Ask about the functions of the externs, the scheduling, etc. before you commit yourself to anything.