When the New York City Education Department announced that it was changing part of its admissions exam for its gifted and talented programs last year, in part to combat the influence of test preparation companies, one of those companies posted the news with links to guides and practice tests for the new assessment.

The day that Pearson, a company that designs assessments, announced that it was changing an exam used by many New York City private schools, another test prep company attempted to decipher the coming changes on its blog.

Assessing students has always been a fraught process, especially 4-year-olds, a mercurial and unpredictable lot by nature, who are vying for increasingly precious seats in kindergarten gifted programs.

In New York, it has now become an endless contest in which administrators seeking authentic measures of intelligence are barely able to keep ahead of companies whose aim is to bring out the genius in every young child.

The city’s leading private schools are even considering doing away with the test they have used for decades, popularly known as the ERB, after the Educational Records Bureau, the organization that administers the exam, which is written by Pearson.

“It’s something the schools know has been corrupted,” said Samuel Meisels, an early-childhood education expert who gave a presentation in the fall to private school officials, encouraging them to abandon the test. Excessive test preparation, he said, “invalidates inferences that can be drawn” about children’s “learning potential and intellect and achievement.”

Last year, the Education Department said it would change one of the tests used for admission to public school gifted kindergarten and first-grade classes in order to focus more on cognitive ability and less on school readiness, which favors children who have more access to preschool and tutoring.

Scores had been soaring. For the 2012-13 school year, nearly 5,000 children qualified for gifted and talented kindergarten seats in New York City public schools. That was more than double the number five years ago. “We were concerned enough about our definition of giftedness being affected by test prep — as we were prior school experience, primary spoken language, socioeconomic background and culture — that we changed the assessment,” Adina Lopatin, a deputy chief academic officer in the Education Department, said.

And yet test prep companies leapt to action, printing new books tailored to the new test and organizing classes.

Natalie Viderman, 4, spent an hour and a half each week for six months at Bright Kids NYC, a tutoring company, working on skills like spatial visualization and serial reasoning, which are part of the Nag-lieri Nonverbal Ability Test, or NNAT 2, the new gifted and talented test. She and her mother, Victoria Preys, also worked every night on general learning, test prep and workbooks, some provided by Bright Kids.

“It is my philosophy that if you can get more help, why not?” Preys said. She prepared her son the same way and he benefited, she said, scoring in the 98th percentile, qualifying him for a seat. She interpreted the Education Department’s decision to change the test and “raise the standards,” she said, as a message that it expected parents to do more. “We are increasing the standards, so you have to work with your kids more, to prep more,” she said.

“Every time these tests change, there’s a lot of demand,” Bige Doruk, founder of Bright Kids, said. She said she did not accept the argument that admissions tests had been invalidated by test prep. “It is not a validity issue, it’s a competitive issue,” she said. “Parents will always do what they can for their children.” And not all children who take preparation courses do well, she said. The test requires that 4-year-olds sit with a stranger for nearly an hour — skills that extend beyond the scope of IQ or school readiness.