State education officials say the funding shortfall is caused by explosive enrollment.

The virtual school's $20 million budget is divided among school systems based on their previous enrollment in the program. The solution will require school systems such as Wake to decide whether they want to tap into already strained local budgets to pay for students to take courses online.

"It's safe to say that there are students who won't be at NCVPS because of the funding shortfall," Philip Price, chief financial officer at the state Department of Public Instruction, said on Monday.

Established by the state in 2007, the Virtual Public School hires state-certified teachers to teach courses online. Students register through their schools to take courses such as psychology or Chinese that they don't have time to take during the school day or that aren't offered at their schools.

Officials have identified 15 school systems that have maxed out the budgeted amount set aside for them to enroll students at the virtual school.

Registration for the spring semester started this month, and officials say enrollment from other school districts also will soon be capped unless they provide their own money.

Price said state law prohibits school districts from charging students to attend the virtual school.

Wake school officials are now identifying which students are most in need of virtual courses to graduate in the spring, according to Greg Thomas, a Wake schools' spokesman. But how much Wake could pay out of its local funds isn't known yet.

Price said the fall enrollment of 17,471 students was nearly 2,000 more than projected. State officials are now projecting 28,251 students for the spring - 3,000 more than originally projected - leaving them $3 million short for teacher salaries.

Price said the projected shortfall would be worse if not for $2 million in reserve funds already set aside to pay for additional students.

Wake has 1,047 students enrolled this fall, more than double what was projected, and it is projected to have 2,111 students who want to enroll this spring. That's nearly triple last year's total. With most courses costing $349 per student, Wake could face an additional $700,000 to meet demand.

Price and Ross White, executive director of the Virtual Public School, said they're working out a way to determine how to allocate the $2 million in reserve funds. They said they're also seeking ways for individual districts who've maxed out their budgeted amount to be able to pay for the spring semester.

Officials hope to allow students in the districts that are now locked out to begin registering this week.

"We're really hopeful that we're going to be able to serve the large majority of the enrollment," White said.