A rash of allegations about sexual misconduct in Gwinnett County schools highlights how difficult it can be to detect and stop relationships between teachers and students before they cross a line.

Three educators in Gwinnett, Georgia's largest school district, have been arrested this school year on sexual misconduct charges. Police are investigating a fourth for allegations she had sex with a 17-year-old boy.

In most of these cases, records show, school officials learned of the allegations after a parent or student reported it. Georgia law requires teachers and school administrators to report suspicions of inappropriate contact, but experts say that doesn’t happen often enough, for a variety of reasons.

It's unclear how big a problem inappropriate teacher-student relationships are, because no one is keeping count. They are handled on a piecemeal basis here in Georgia and across the nation. The Atlanta Journal-Constitution took at look at the issue here and talked to experts who explain what happens when teachers cross the line.