CHICAGO — To graduate from a public high school in Chicago, students will soon have to meet a new and unusual requirement: They must show that they’ve secured a job or received a letter of acceptance to college, a trade apprenticeship, a gap year program or the military.

Mayor Rahm Emanuel (D) said he wants to make clear that the nation’s third-largest school system is not just responsible for shepherding teenagers to the end of their senior year, but also for setting them on a path to a productive future.

“We are going to help kids have a plan, because they’re going to need it to succeed,” he said. “You cannot have kids think that 12th grade is done.”

Few would dispute that kids often need more than a high school diploma to thrive in today’s economy, but there is a simmering debate about the extent to which schools should be — and realistically can be — expected to ensure their graduates receive further training.

Emanuel’s plan, approved by the Board of Education in late May, has planted Chicago at the center of that debate.

Experts say Chicago Public Schools is the first big-city system to make post-graduation plans a graduation requirement. But the question is whether the cash-strapped district can provide enough mentoring and counseling to help its neediest students succeed when the rule takes effect in 2020.