DENVER (AP) — The Denver Public Schools and its striking teachers reached a deal Thursday to end their three-day walkout, with raises of 7 to 11 percent, built-in cost-of-living increases and more opportunities for future salary hikes.

A key sticking point -- variable bonuses for working in tougher environments -- will be studied to see if they help retain teachers in schools, the teachers' union said.

The deal was reached after marathon negotiations and announced shortly before schools opened Thursday morning. Teachers were encouraged to return to their classrooms if they feel ready to, even though the deal awaits ratification by the full union membership.

More than half the district's teachers went on strike Monday after negotiations over pay broke down.

A key sticking point was the teachers' demand that the system rely less on bonuses for educators in high-poverty and high-priority schools.

The district gives bonuses ranging from $1,500 to $3,000 a year to teachers who work in schools with students from low-income families, in schools that are designated high priority or in positions that are considered hard to staff, such as special education or speech language pathology. It sees the bonuses as key to boosting the academic performance of poor and minority students.

The union says the bonus question, which its lead negotiator, Rob Gould, called "the elephant in the room," will now be studied.