For 13 years, Adriana Aviles, a fierce education advocate and former NYPD cop, has been the ultimate insider in New York City schools. As a powerful leader on the Citywide Council on High Schools, she championed Queens District 26 as one of the best in the city. She knew the principals and the teachers — and trusted them. She was gratified that her son consistently received good grades, especially in math, throughout his K-8 years. Then, two weeks ago, she sat down with her 14-year-old son to help him review for his second high school math exam. What happened next left her stunned and her son in tears — and prompted her to publicly confront Schools Chancellor Kamar Samuels at a town hall last week. She shared her family’s devastating experience with The Post’s David Spector.