OAK BROOK, Ill. – Two boxes of french fries stacked on the kitchen floor, rather than stored in a freezer. An empty salt shaker at the fry station. A dry, unseasoned cheeseburger served on a hardened bun.

Those are just a few of the problems a McDonald's manager is expected to spot in this mock kitchen. If they miss them, it's probably a good bet that they won't be making the dean's list at Hamburger University in this Chicago suburb, where managers are graded on everything from handling ­customer complaints to hiring the best workers.

Each year, hundreds of new McDonald's U.S. general managers spend five days at Hamburger University on the burger giant's corporate campus, working toward an honorary bachelor's degree in Hamburgerology. During their visits, they role play, have meetings with their boss — in this case, a professor — and prepare to return home and make real improvements at the restaurants they run.

"If you think about it, each of them is running a multimillion-dollar business," said Rob Lauber, vice president and chief learning officer of McDonald's Restaurant Solutions Group. "So we want to make sure they have good business grounding."

Every GM makes a run through Hamburger U, taking courses that include shift ­management, introduction to management and guest ­services before they get to the session known as GM Capstone. There are classes for other leaders as well.

"We put a little bit of pressure on them to quickly make their decisions, just like they do back home," said Jason Hamm, McDonald's national training manager. "We try to throw a lot of different things at them."

Hamburger University opened in 1961 and has seen some 330,000 students take its courses around the world. But the need for training is especially urgent now as McDonald's pushes to turn around its U.S. business, which has seen comparable sales and customer visits slip for two consecutive years. Average sales at a McDonald's U.S. restaurant fell to nearly $2.5 million in 2014 after exceeding $2.5 million a year earlier.

On April 1, McDonald's pledged to bolster educational opportunities for U.S. workers, including covering costs for certain high school and college courses. In making the announcement, which also includes wage increases at the company's own U.S. restaurants, CEO Steve Easterbrook noted that focusing on people held the key to a turnaround.

"A motivated workforce leads to better customer ­service," he said.

The late Fred Turner, who rose from working as a griller to McDonald's senior chairman, started Hamburger U in the basement of a McDonald's in suburban Chicago. Fifteen students graduated from the first class in February 1961. There are seven Hamburger Us around the world, including the newest in Shanghai, which opened in 2010.

Numerous McDonald's executives have taken courses at Hamburger U, including McDonald's USA President Mike Andres. Easterbrook took operations training at the school's London location. Overall, 40 percent of McDonald's global leadership has attended the school.

At the 130,000-square-foot learning lab in Oak Brook, called the Fred L. Turner Training Center, general managers learn leadership, teamwork and decisionmaking skills in classroom and restaurant settings. Ninety to 120 GMs graduate from each session of GM Capstone, which is set to be held about 20 times this year.

Franchisees pay $145 for a staff member to take the course, and also pay for flights, meals and accommodations.

During a recent class, students tried to identify what was wrong with a cheeseburger, fries and a smoothie. They have set amounts of time to complete their tasks, such as computerized scheduling sessions in which they adjust staffing levels to meet sales, labor and profit goals. Students must come up with plans before presenting them to the professor in both oral and written form.

McDonald's is not alone in running corporate training for managers. Companies such as Farmers Insurance and General Electric have their own training centers. But McDonald's has some unique problems as it trains its own employees.

"Early on [McDonald's] realized that each of [its] stores needed somebody who not only had skills, but had judgment," said Elliott Masie, chairman of the Learning Consortium, 230 companies that run a research collaborative focused on workforce learning. Companies in the Learning Consortium include McDonald's, Starbucks, Google, Microsoft and Wal-Mart.

As part of his work, Masie has studied Hamburger U and other corporate training efforts. Some, which he declined to name, are more like the "Club Med of learning," Masie said. He said McDonald's has a different reputation. "They bust them there. It is a rigorous academic and interpersonal piece of the puzzle at McDonald's."

Stephen Jones, the 29-year-old manager of a McDonald's blocks from Yankee Stadium in New York City, called his week at Hamburger U "a once-in-a-lifetime opportunity."

"I really get the chance to sit back and take a look at the business itself and reanalyze the way I run operations back at home," he said.

Jones, like others, has seen McDonald's go through difficult times before. But he's optimistic the company can again find its way.

"We have to do what we're supposed to do, and that's focus on the customer," Jones said.