Only 54 percent of city students who qualified for spots in gifted and talented programs received offers for this fall, compared to 73 percent who were offered placement last year.
The Department Of Education partly attributes the decline to a rise in applications.
DOE officials also did not guarantee a seat for every student in his or her own district, saying many families decided against accepting offers in past years.
Education officials stressed the gifted and talented classes are just one option for students, who also can use other programs at their schools.
The DOE used a new test that was supposed to be more difficult, but more students qualified for gifted and talented programs.
The process was delayed by almost a month, after parents discovered errors in the score calculations.
DOE officials said Pearson, the company administering the tests, is responsible, and the city is reconsidering its contract with the company.