Nearly half of the de Blasio administration’s Renewal high schools did worse at preparing their students for college last year than they did the previous year, a pro-charter group charged.

Families for Excellent Schools said it reviewed public data from the 34 high schools that the mayor’s Education Department identified as the most failing and targeted for improvement in 2014.

Of that group, 15 of the schools declined in terms of college preparedness last year.

“Mayor de Blasio’s refusal to admit that his School Renewal program has failed is keeping thousands of kids off the path to higher education,’’ the group said in a statement, arguing that this is yet another reason for Hizzoner to not fight new charters.

The city Department of Education said that the lobbying group was misstating the facts, and that data show the schools have, in fact, improved.

“Despite its inaccuracies, this report correctly recognizes that a majority of Renewal high schools increased their college-readiness rates last year,” said DOE spokesman Will Mantell.

David Bloomfield, a professor of education at Brooklyn College, said the pro-charter group often “bottom feeds numbers that don’t mean anything.”

He added it’s impossible to give a clear snapshot of how a school is doing in just one calendar year.