BOISE, Idaho (AP) — Idaho officials say alternative and virtual charter high schools are dragging down the state's graduation rate.

State Board of Education President Don Soltman told a legislative budget writing committee Monday that alternative schools have a 36 percent graduation rate. Meanwhile, virtual charter schools have a 20 percent graduation rate.

Soltman says those low numbers are the main reason why Idaho's overall high school graduation rate had recently plummeted from roughly 83 percent to 77 percent.

Public schools still maintain an 88 percent graduation rate, and district-authorized charter schools boast the highest graduation rate at 91 percent. Soltman said the board has been researching the cause of Idaho's low graduation rate ever since the new numbers were released in December.

He added that they will use the information gathered in their research to improve graduation rates at the under-performing schools.