A sticking point was whether Lynn Abraham washed the boy's mouth out with soap or if she just wiped outside it.
The 4-year-old was notoriously difficult, swore often and the final straw was when he called a teacher a "stupid b****".
The daycare centre manager took him to the bathroom to wash the bad language away.
Abraham was sure she never washed inside his mouth.
But why then, asked the prosecution, was another teacher shocked and Abraham given a verbal warning if she just cleaned his face and hands?
The jury wasn't convinced.
The 59-year-old this week defended 11 charges of assaulting children, all under 5, in a jury trial at the Auckland District Court.
After five hours of deliberations, the jury found her guilty of all counts except taping a girl's mouth because she was being noisy.
The offending occurred while she was the manager at the Bright Minds Daycare Centre in St Johns from 2011 and continued through until last May.
She was charged with smacking children in her care - not to prevent them from being disruptive or to stop them harming themselves or others, but out of frustration or to discipline them.
And prosecutor Brian Dickey said that was against the law.
The Crimes Act says a parent or person in their place is justified in using force under a certain set of circumstances.
But what it didn't permit, said Dickey, was hitting children with a smack so hard other staff members could hear it or striking them and saying they had "nothing to cry about", as one witness had claimed.
"You don't get to smack kids to give them something to cry about. That's gratuitous."
The prosecutor painted a picture of a pattern of offending which presented itself when Abraham was stressed or frustrated which worsened over the years.
A former teacher, Ines Miranda, said the smacks would happen once a fortnight but became more frequent when Abraham was more stressed.
"I can feel when a [person] feels very stressful, I can pick it up very easily."
She told the court, Abraham had "no control" over herself.
Yet, Abraham denied the alleged incidents ever occurred.
Though if she did hit children, she said it was only ever to tap or flick hands to prevent them hurting themselves or another child.
She conceded under cross-examination it was "possible it could have been seen as a smack", and demonstrated slapping the back of her hand.
Abraham admitted she "might" have smacked three of the children but given how many years had passed, couldn't recall the specific incidents.
The manager was adamant though she never washed inside the boy's mouth to punish him for swearing.
"I washed his mouth and I'm indicating on the outside of his mouth, I did not wash inside his mouth."
As she did so, Abraham said, she told him they were doing that to wash "away the bad words".
The manager called her former boss, who has name suppression, and told her about the boy's swearing as it happened in front of some parents.
The woman said Abraham told her she then washed his mouth "out" with soap. At which point, she stopped her and said: "At what level do you think that's okay? How could you possibly think you could do that to a child?"
Abraham was given a written warning, which she acknowledged with a signature, though the document didn't include details of the warning itself.
But despite her certainty that the incidents never happened, her words had been misheard or that her force was justified, the jury decided she was guilty.
The only charge they couldn't convict her on was that she'd taped a girl's mouth.
The jury heard from another teacher, Jennifer Wong, who said in December 2012 one of the children was playing noisily outside.
Abraham went out and told her to be quiet and threatened her with tape.
When the girl continued to be loud, Abraham allegedly went outside and put tape across her mouth and left it there for about five minutes.
But the manager said that never happened and the jury was convinced.
However, they didn't believe her testimony that she didn't force-feed the children.
A very upset and emotional Wong told the jury how one of the more difficult children would spit out his food so a frustrated Abraham would pick it back up and force it into his mouth.
Using her hand, Wong showed the court how Abraham would then hold it over their jaw and force them to chew.
Again, Abraham denied this.
Her former colleague, Mary Stoddard who is now deceased, backed her up.
In her statement she said there was one older child who they had trouble getting to eat his lunch so "Lynnie" fed him with a spoon and [would] say "eat up".
"We even have to spoon feed some of them, we don't force-feed them."
But the jury were unconvinced and convicted Abraham on this charge too.
Both sides depended heavily on propensity evidence - did a teacher's account that Abraham frequently smacked when she was frustrated or angry mean she was more likely to be guilty of the assaults?
Or was the parents' testimony - including a couple whose son was named as a victim - that Abraham was caring, kind and firm but fair enough to convince the jury her force was probably reasonable in the circumstances?
In his closing, Dickey said the parents who gave evidence for the defence that Abraham was "firm but fair" and the centre was a happy place were irrelevant.
They didn't actually witness the alleged offending.
But neither did the other teachers, said defence lawyer Graeme Newell.
Before they were sent to decide Abraham's fate, he told the jurors the only evidence came from "a single witness in what was a very busy childcare centre populated by a number of adults".
"Can you reply upon the evidence on that sole witness in accepting that charge?"
It seems it was enough.
After five hours and two questions to Judge June Jelas, the jury found Abraham guilty on all but one of the charges.
And as the foreperson read the verdicts, the former manager stood quietly in the dock dressed in a knitted cardigan.
THE CHARGES AND VERDICTS:
Put tape on a 4-year-old girl's mouth - not guilty
Smacked a child under 5 on the hand - guilty x6
Washed a 4-year-old's mouth out with soap - guilty
Force-fed a child - guilty x3