(AP) Walmart is extending its debt-free college benefits to high schoolers as a way to attract and retain workers in a tight labor market. The nation's largest private employer says it will offer free college SAT and ACT prep for its workers in high school, while offering two to three free general education college classes through an educational startup. Walmart estimates about 25,000 people under the age of 18 work at its stores, a fraction of its 1.3 million person U.S. workforce. The enticements mark an expansion of a program Walmart launched last year that offers affordable access to a college degree. The company is working with Denver-based Guild Education that offers a program costing a dollar a day at several non-profit universities.