Most parents and students are in the dark about how much college costs.

That's the main takeaway from the latest data in an ongoing study by the National Center for Education Statistics, part of the Education Department's research division.

Only around 10 percent of ninth graders correctly estimated the tuition and fees for one year at a public four-year college in their state. Around 57 percent overestimated the costs, and 32 percent underestimated them.

Across the board, students' forecasts were off by an average of $10,500, and parents by $8,800.

Some 26,000 students who were in ninth grade in 2009 were followed and interviewed throughout high school, college, their work-life and beyond. Their parents were also questioned.