The U.S. Supreme Court, the letter notes, ruled that undocumented children living in this country can't be barred from attending public elementary and secondary schools because of their immigration status.
New Jersey law stipulates that domicile and age are the only registration eligibility factors, the letter states.
There are also immunization requirements, but the state will allow some flexibility in meeting those requirements.
Last month, the ACLU sued the Butler School District in Morris County, alleging it was denying registration to immigrant families who could not provide official photo IDs. The district at first declined to change its policy but then relented.
As a result of the Butler case, the ACLU said, they decided to survey the state's districts - not because they had received complaints about those districts.
The ACLU's letter sent out last week says districts have four weeks to change their policies, or risk getting sued.
Of the 136 districts cited statewide - close to a quarter of all districts - 34 were in the three-county South Jersey area. The letters went out to districts in communities ranging from small, like one-school National Park, to large, like Camden and Cherry Hill.
Most of the districts did not get letters until Thursday or Friday. Several, including Cherry Hill, referred the matter to lawyers and declined comment.
Individual schools in Camden appear to have varying requirements.
"The new administration is reviewing the district's enrollment policies and will, of course, ensure our policies are compliant with state and federal law," district spokesman Brendan Lowe said.
Some superintendents said they weren't aware that photo IDs were being required by their districts and expressed willingness to make the changes requested by the ACLU.
Other forms of ID
"We are removing it," said Michael Livengood, superintendent of Maple Shade's schools, adding that children have not been refused registration over lack of photo ID.
Mount Ephraim will also amend its policy, said Superintendent Leslie Koller, but she added that her staff already accepts other forms of identification and that children were not kept from registering.
Children have not been turned away in Oaklyn, said Scott Oswald, superintendent since 2012, who is also superintendent of the Collingswood schools. Collingswood did not get a letter.
"My guess is if there is something listed in the registration materials for Oaklyn, it's been there for decades," he said. "We have 1.2 million laws, codes, and regulations to follow. This one may not get a lot of attention. If we have something on our registration forms that requires a photo ID, it will be removed."
Some superintendents said asking for a photo ID served a security function that would be missed.
'To make sure'
"It does concern me because we don't want to deny anybody's rights, but we want to make sure we're safeguarding the student," said Michael Gorman, Pemberton's superintendent, who said no child had been refused enrollment over lack of a photo ID.
In Pemberton, he said, a copy of the guardian's photo ID is kept as part of the child's permanent record, helping to inform matters such as whom the child can be released to.
Newlin Schoener, superintendent of the Waterford schools, where the immigrant population is very small, had a similar view.
"We want to be sure that the adult is who they say they are," he said.