Administrators at an Upper West Side elementary school didn’t know the checkered history of a staffer charged with sexual abuse last week because he hadn’t been reprimanded in writing, Schools Chancellor Dennis Walcott told parents yesterday.

At a meeting packed with nearly 500 parents at PS 87, Walcott said he would address the communication glitch that allowed the school to hire teachers aide Gregory Atkins without knowing he had acted inappropriately with a student in 2006.

An investigation at the time concluded that Atkins improperly spent time with the MS 322 student outside of school and buying him gifts — including a jock strap.

It found no sign that the relationship was sexual, according to the Department of Education.