Colorado has launched a program to train 20,000 apprentices in the next decade. Students attend high school three days a week, and work at paying jobs two days a week in information technology, advanced manufacturing, and other sectors. Over three years, students will earn both their diplomas and some college credit, along with workplace skills. Colorado has modeled the program after Switzerland’s widely respected apprenticeship system, but some activists doubt that U.S. employers and high schools will make the commitment necessary for the program to work on a large scale here.