SAREX stands for Shuttle Amateur Radio EXperiment. This is the Shuttle Amateur Radio Experiment program operated by AMSAT in cooperation with NASA. NASA's own website explains SAREX here. Under this experimental program, space shuttle crew who are also licensed amateurs are allowed to take radio equipment into space. Hundreds of contacts with amateur stations on the ground ensue and radio amateurs around the world get involved with space communications.
The AMSAT project to involve schools in many SAREX experiments has been very successful and has opened the eyes and the imagination of many school students to both space travel and to amateur radio.
ARISS - Amateur Radio on the International Space Station
This project uses amateur radio to link school students with astronauts on the ISS. More details can best be read at the AMSAT site.