City Comptroller Scott Stringer is demanding the Administration for Children’s Services prove it’s instituting promised reforms — after a mom on the agency’s radar allegedly murdered her baby.

“In the wake of another tragic death of a child apparently known to ACS, it is imperative that you make clear the steps that ACS is taking to implement the recommendations,” Stringer wrote Friday in a letter to the troubled agency’s new commissioner, David Hansell, which was leaked to The Post.

Agency workers had visited synthetic marijuana-addicted mom Joann McLeod, 30 — who had already lost custody of three kids for neglect — just three weeks before she allegedly threw 5-month-old Raymond Porfil Jr. against a wall and he later died.

It’s been six months since the agency’s independent monitor, Kroll Associates, issued a report recommending an overhaul following the deaths of several other kids known to ACS.

The agency said it would make the changes early this year — but is yet to provide any updates, according to Stringer.

The changes highlighted include broadening the number of ACS staff who can see criminal-history records, reducing response times and coordinating better with the Department of Education.

An agency spokeswoman says it has already contacted Stringer to set up a meeting for an update, but notes all of the reforms “are either completed or well underway, and many of them were already underway before Kroll issued its report in December.”