Parents of public school children yesterday got a new best friend at City Hall.  

Martine Guerrier, an outspoken Brooklyn mom of a fifth-grader, was tapped as the city’s first parent czar in a move apparently designed to deflect a barrage of criticism that school officials haven’t been listening to parents.

Guerrier, 36, wasted no time in taking on the Department of Education, telling reporters exactly what she thought about last month’s school bus fiasco that stranded thousands of kids on frigid city streets.

“The department has recognized an error in that, and I don’t know that that decision would have been made the same way had there been a parent at the table,” Guerrier said. She vowed not to be a pushover or abandon her independent stance as Chief Family Engagement Officer, which pays $150,000.

“The only difference is that I’ll probably smile more when I say, ‘No, I don’t agree,'” she said.

The announcement came just hours before a noisy, overflow crowd of 1,000 parents and activists (including members of Make the Road by Walking) crammed into St. Vartan’s Cathedral on the East Side to protest the Education Department’s wide-ranging reorganization plans.

“It’s chaotic and destabilizing for parents, teachers and students,” shouted Tim Johnson, president of the Chancellor’s Parent Advisory Council.

Guerrier often challenged the administration as a member of the city’s Panel for Educational Policy. She voted against the mayor’s policy to hold back underachieving third-graders and abstained from voting on a similar measure for fifth-graders.

Klein and Bloomberg both insisted they weren’t bothered by an independent voice. “Having a diverse range of views is great,” Bloomberg said. “I value her independence and candor.”

Brooklyn Borough President Marty Markowitz, who appointed Guerrier to the panel and founded Best of Brooklyn Inc., a nonprofit where she currently works, said Guerrier “has shown … you can be a ‘can-do person’ without being a ‘yes-person.'”

Some advocates were skeptical of Guerrier’s new role, writing it off as window dressing and complaining there was no public input in the selection.

“It unfortunately is another example of what the system’s stakeholders are angry about, which is lack of consultation before new initiatives are announced,” said Bertha Lewis, co-chairwoman of the Working Families Party.