Mayor de Blasio’s plan to offer ­algebra to all eighth-graders and Advanced Placement courses to all high-school students ignores how far behind most students are on the basics, educators and advocates say.

Forty-one percent of eighth-graders who took this year’s state math tests scored at the lowest level, which means they’re not close to being on grade level, let alone ready for advanced math.

Similarly, the mayor’s AP proposal in high schools didn’t include a component to prepare kids for the higher-level work.

“How are they going to be able to deal with algebra if they can’t deal with the math curriculum they have now?” asked Frank Cimino, who retired as principal of PS 193 in Brooklyn in 2013.

The mayor’s initiative, which is being phased in over six years, also promises computer science courses for all students by 2015.

However, Hizzoner said on Friday for the first time that the effort would integrate the computer-science matter into the course work of other classes, rather than require it to be taught as a stand-alone subject.

Asked about the critiques, city education officials said the algebra initiative would include expanding summer school and teacher training.

They also said AP prep would include summer school, writing workshops, Saturday review courses and mock exams.