"Just Do It" has been a familiar Nike slogan for years, but some parents are wondering what it was doing on some of New York's Common Core standardized English tests.

Brands including Barbie, iPod, Mug Root Beer and Life Savers showed up on the tests more than a million students in grades 3 through 8 took this month, leading to speculation it was some form of product placement advertising.

New York state education officials and the test publisher say the brand references were not paid product placement but just happened to be contained in previously published passages selected for the tests.

Some critics aren't so sure and questioned why specific brand names would be mentioned at all.

"It just seems so unnecessary," said Josh Golin, associate director of the Campaign for a Commercial-Free Childhood, which monitors marketing directed at children.

"It would be horrible if they were getting paid for it," he said. "But even if they're not, it's taking something that should not be a commercial experience and commercializing it."

The test questions have not been made public, and teachers and principals are barred from discussing them. But teachers posting anonymously on education blogs have complained that students were confused by the brand names, which were accompanied by trademark symbols.

The Nike question was about being a risk taker and included the line, "'Just Do It' is a registered trademark of Nike," according to students who took the test.

Sam Pirozzolo, of Staten Island, whose fifth-grader encountered the Nike question, said there was apparently no reason for such a specific brand.

"I'm sure they could have used a historical figure who took risks and invented things," Pirozzolo said. "I'm sure they could have found something other than Nike to express their point."

Deborah Poppe, of West Hempstead, Long Island, said her eighth-grade son was similarly puzzled by a question, which drew complaints for a second straight year, about a busboy who failed to clean some spilled root beer — Mug Root Beer, to be exact, a registered trademark of PepsiCo.

'"Why are they trying to sell me something during the test?'" she quoted her son as saying. "He's bright enough to realize that it was almost like a commercial."

The use of brand names was one of several complaints raised by some educators and parents about the statewide tests, aligned to the Common Core standards intended to increase academic rigor. Some contend they are too difficult and don't measure what students are actually learning.

While such general complaints about Common Core tests have arisen elsewhere, advocates said the prevalence of brand names appears to be specific to New York.

Representatives of the New York State Education Department and Pearson, the education publishing giant with a $32 million five-year contract to develop New York's tests, said the companies did not pay for the exposure.

"There are no product placement deals between us, Pearson or anyone else," said Tom Dunn, an Education Department spokesman. "No deals. No money. We use authentic texts. If the author chose to use a brand name in the original, we don't edit."

Pearson spokeswoman Stacy Skelly said neither the company nor the education department received any compensation for the mentions. And if any brand comes up in a passage, she said, "the trademark symbol is included in order to follow rights and permission laws and procedures."

Nike and Wrigley, the maker of Life Savers, said they were unaware they were mentioned on the tests. Other companies declined to comment or did not return messages.

Some advertising experts said the idea of product placement on a test is inappropriate and fraught with peril.

"If any brand did try to place there, what they would lose from the outrage would surely trump any exposure they got," said Michal Ann Strahilevitz, a marketing professor at Golden Gate University.

Kelly O'Keefe, a marketing professor at Virginia Commonwealth University, said he is a fan of brands, but there are places where they don't belong.

"Education, religion and civic life are places where brands are unwelcome," O'Keefe said. "It would be wise for Pearson to avoid using brands in their testing even if they're not paid for by the brand itself."

Others endorsed the position of New York state educators — that brand names belong on the tests because they are part of the world students inhabit.

"Brands are part of our lives," said Allen Adamson, managing director of the New York brand consulting firm Landor Associates. "To say they don't belong in academia is unrealistic."