FORT WORTH (CBSDFW.COM) – When Zachary Henderson pitches a fit, strangers see bad behavior. His mother sees something else.

“I think I was in denial for a long time,” said Rachel Henderson.

A doctor at Cook Children’s Hospital diagnosed Zachary last year with Pervasive Developmental Disorder, or autism.

“Zachary will need more one-on-one attention and small group learning,” read the doctor’s notes.

So, when the then five-year-old started kindergarten at Sendera Ranch Elementary School, his mother asked he be designated as a special education student.

“I would really like them to recognize the fact that Zachary has a disability,” she said.

The Northwest Independent School District tested Zachary, who’s now six.

An autism assessment team, though, found he didn’t appear to be autistic at all and was not eligible.

“As long as they’re being successful and performing at or above grade level, which this child is, there’s not an educational need to provide additional services,” said Lesley Weaver, an NISD spokesperson.

Henderson disagrees. In a regular class setting, she says her son becomes a target for his occasionally odd behavior.

“Kids saying he’s bad or making fun of him… it’s very difficult,” she said.

At the Child Study Center in Fort Worth, Dr. Joyce Elizabeth Mauk, said autism is difficult to diagnose, even for professionals.

“It’s not uncommon for medical personnel and school personnel to come up with different diagnoses,” Mauk said.

Because the severity of autism can vary so widely, she also said there’s no one solution for how to best accommodate students who may be struggling with it.

Henderson has requested a second opinion, and NISD said it will cover the cost of an independent evaluation by another group of experts.

Other school districts have similar policies allowing parents to contest a school’s findings.

Federal law also dictates parents have a right to take the matter before a judge or file a complaint with the Department of Education.