Ashburton College principal Ross Preece said the report could not be released due to privacy.
He also would not respond to further questions around both the investigation and Deuart's concerns.
The college commissioned an investigation because Preece said there had been concerns raised about the special needs learning unit.
Preece, in a written statement, said the report proved that none of the allegations had been upheld.
"In term two of 2021, Ashburton College received a complaint regarding allegations of staff bullying within Te Whare Manaaki," Preece's statement said.
"The college instigated a comprehensive independent investigation into the complaint, which has now been completed.
"Due to privacy reasons, the investigation report cannot be disclosed. However, the investigation has highlighted that whilst there have been some working relationship issues identified between the staff in Te Whare Manaaki, none of the allegations of bullying were upheld.
"The college is committed to continuing to provide its students, staff and whānau a safe, supportive learning and working environment."
Deuart first became concerned during a visiting day in November 2020 where she claims she saw the teacher grab her son's hand and squeeze it "violently" until he answered her.
The mother's second complaint came after indications from her son that the teacher may have encouraged him to "keep secrets".
She was interviewed as part of the investigation but had not seen the report and was not informed of its findings.
"I just think it is a big joke," Deuart said.
Former teacher aide Porsha Coley also claimed she had witnessed what she considered physical and emotional abuse toward pupils from a teacher in the unit.
She left earlier in the year because she was fed up with the alleged inaction from school leaders around the unit.
Emails obtained by Local Democracy Reporting dating back to 2019 detailed other concerns from staff members.
