About half of Tennessee counties still need volunteers to mentor the record number of high school seniors who applied for the state’s tuition-free community college program, prompting the state to extend its deadline.

As of Tuesday, Shelby County had the greatest shortage and needed 509 more volunteers to serve as mentors for Tennessee Promise, the state’s pioneering program to get more students to attend in-state community or technical colleges. Home to the state’s largest school system, the Shelby County also had the most students apply: about 8,650.

In all, 44 of Tennessee’s 95 counties still need volunteers, although some, like Campbell County, need as few as one. Last Sunday’s deadline has been extended to Dec. 1 for volunteers in those counties to apply, according to a spokeswoman for TNAchieves, the nonprofit organization that coordinates the program.

Other counties had substantial surpluses in volunteers and have closed applications. Nashville’s Davidson County, for example, has a surplus of 296 volunteers.

Statewide, about 61,000 high school seniors have applied for Tennessee Promise. They’ll go through a nine-month process of qualifying that includes working with an adult mentor.

Research shows that mentor relationships help students not only enroll in college, but finish. On average, Tennessee Promise mentors spend about an hour a month working with up to seven students as they transition from high school to college, reminding them of important deadlines, encouraging them, and serving as a trusted resource. Mentors must be at least 21 years old and attend a one-hour training and two one-hour meetings with their students over the course of a year.

When Tennessee Promise launched in 2014, Tennessee became the nation’s first state to offer two years of community or technical college free of tuition and fees. Even as the state struggles with college preparedness, it’s seen a boost in college enrollment.