This was a teacher making an effort to bond with a struggling student. Or was there more to it? The historic case heard in the County Court last month was the first trial involving a new single offence: grooming, without any sexual assault. This is what Nathan was charged with in August 2015. What has happened since then amounts either to the destruction of an innocent teacher's reputation – or the failure of the legal system to protect a vulnerable child. What is not in dispute is the trial reveals the complexities of a new law designed to address a very old problem.

What the court was told According to the prosecution, the concerning behaviour began when Nathan started rewarding Jack with special trips. They went to the movies. After Jack graduated from primary school, and enrolled in a new secondary school, the excursions became a weekly affair: Timezone, Build-A-Bear and roller derby. Over time, the day trips turned into night outings. At some point, Nathan started to give Jack gifts. A teddy bear, Adidas sneakers, and a Playstation 3. All easily explained, said the teacher's barrister. Nathan felt sorry for the boy. He was being raised by a single mother, who supported her many children on a pension. There was little left over for luxuries, or even treats.

And Jack's mother was happy with their friendship – to start with anyway. The boy was raised in a violent household. When Jack was in his final year of primary school, his father, who had been in trouble with the law, left home. After that, the boy unleashed on his mother. He swore at her and threw tantrums, she told the court. He stole her credit card, and lied to get out of trouble. He could be inappropriate – a female teacher claimed he once asked her if a penis had ever touched her G-spot. But Nathan, it seemed, could get through to the troubled teenager. Jack confided in him, and texted him often, addressing his old teacher as "big bro".

Jack confessed by text when he did something wrong, like stealing his mother's credit card. Nathan, in turn, would gently reprimand the boy. "Remember good choices we talk about," he texted. Jack's mother had no qualms about the daily texts between the pair or the playdates. The texts did not appear untoward, she told the court. She trusted Nathan. She wanted a positive male role model for her son, who she worried was turning into his father. Then on November 3, 2014 Detective Senior Constable Jodie McManus from Dandenong Sexual Offences and Child Investigation Unit (SOCIT), knocked on Nathan's bungalow door. After interviewing the teacher at Hastings police station, police searched his house. They found photos of Jack on the cupboard in the kitchen.

The grooming law was introduced in 2014 to stop abusers before they harmed children. Before that, grooming could only be considered an "aggravating factor", not a crime in its own right. The reforms were introduced after recommendations from the Victorian Government's Betrayal of Trust report, seven years after New South Wales made grooming a crime. An additional offence taking effect on July 1 will target attempts to "encourage" a child to engage in a sexual act, by asking a child to masturbate or watch pornography. What the new law says The current offence forbids adults from communicating with children under 16 in person or online in an effort to set them up for a sexual act. It also prevents predators from grooming another adult to access a minor in their care. The communication needn't be sexual or involve a sexual act. It requires proof of perverse intent. That's the tough challenge facing prosecutors trying to get a conviction. Few these days dispute the need for grooming offences. Time after time, victims testifying at the federal child abuse royal commission have described the creation of special friendships, the insidious, incremental exposure to sex, nudity and pornography, and the targeting of vulnerable children.

But critics argue that the broad wording of the current law risks criminalising friendships between adults and children. Teachers, youth workers, counsellors, foster parents and sports coaches face an ugly possibility: might an effort to make a child feel "special" be taken as evidence of a crime with a maximum penalty of 10 years in prison? At Jack's school, teachers socialised with students off campus and outside school hours. Breaking barriers was a way of connecting to students, one staff member told the court. The school's wellbeing officer – the person in charge of student welfare, which includes monitoring and reporting child abuse – spent an afternoon with Nathan and Jack at a recreational centre one weekend in 2014. She also joined the pair at the movies. She was aware of the Playstation 3. She saw Jack hang off Nathan's neck while they went swimming. She knew Nathan referred to the boy as his "sidekick". No questions were asked, or reports filed. Not yet. Teachers are now subject to strict new rules: they should not be alone with a child; contact children or their families outside school without the school's consent, create "special relationships" with students or have "unnecessary" physical contact.

Griffith University's Professor Patrick O'Leary, who led the royal commission report on grooming, said adults could give children extra support, or pay them "particular attention", even in a manner that could be viewed as crossing a boundary, without this being grooming. He said touch should not be banned between teachers and students in "some sort of fundamentalist way", particularly with young children. "Touch is a human condition," he said. "We can become overly anxious and think that every potential touch is a potential issue of sexual abuse." Children often sense when they are being inappropriately touched, said Centre Against Sexual Assault's spokeswoman Carolyn Worth. "You want to keep the communication channels with children open so they can tell you these things."

Jack started feeling uneasy, or "yuck", during sleepovers at Nathan's house, the court heard. By this point, he was in year 7, and at a new school. Nathan's version goes like this: He does not deny the boy slept at his house, on a blow up mattress in the lounge room. Nor does he deny they watched movies together on the mattress. He did not put his arm around the boy. They were not at any point "spooning", as the prosecution claimed. Yes, the boy showered at his place, with the door locked. "There were no overtures about a normal act of cleanliness," his statement read.

Now for the prosecution's account: During the movie-watching sessions on the blow-up mattress where the boy slept, the former teacher lay down next to Jack under the blanket, almost touching him. Another time, he put his arm around the boy. One time in the car, the teacher told the boy he had kidnapped him for the day and was taking him to his rape dungeon. (The teacher denied this in court, alleging the boy claimed he would tell police he was "kidnapped" if they got pulled over. The teacher told Jack's mother he had said this at the time. The "rape dungeon" reference may be from a computer game, he said.) A mother becomes anxious Around this time, Jack started obsessively cleaning his room. His mother was suspicious and asked if something was wrong. Eventually, he told her he was "getting … a lot of affection" from Nathan. He said the teacher gave him tips on how to masturbate.

During one sleepover, Jack asked Nathan if he was a virgin, and whether he had a condom, the prosecution said. The boy then blew up the condom "like a balloon". That was the last night Jack slept at his old teacher's house. Jack's mother cut off their contact and called police to seek advice. The relationship was not sexual, she told police, but her son and his former teacher were going on outings and having sleepovers, and she noted the gifts. The boy was interviewed by police, but he wasn't initially forthcoming about the allegations. Jack was angry at his mother for contacting police. He accused her of "imagining things". The teacher denied allegations about the condom and masturbation advice. He did, however, send a Facebook message to Jack's mother in 2014 (they were in regular contact), claiming if jokes made on one weekend with Jack were taken seriously, "my world would fall apart".

The jury was asked to navigate two radically different portrayals of the teacher-student relationship: a "brotherly" bond or a sexually-charged bid to prey on a vulnerable teen. After 25 minutes of deliberation, the 12 jurors acquitted the teacher. The jury's decision raises the question: how much of the acquittal was driven by the difficulty in proving grooming without any suggestion of an actual sexual assault? If we borrow a checklist for grooming laid out by the recent royal commission on the topic, Nathan ticked some of the boxes. Were there gifts? Check. A trusting relationship? Check. Was the victim vulnerable? Check. But even the commission's report described the criminal behaviour as a grey zone. Grooming consists of "many discrete acts", which, on their own, might not be criminal or abusive. It could occur during an "otherwise normal relationship with a child", the report warned.

Greg Barns, barrister and spokesman for the Australian Lawyers Alliance, said Victoria's current grooming law – which targets communication "by words or conduct" – risks taking a "sledgehammer" to adult and child friendships. "Would simply looking at a child for more than a second be considered conduct?" he posed. Australian Childhood Foundation's chief executive Dr Joe Tucci said that criminalising grooming might be complex, but its seriousness should not be overlooked. Grooming laws had to be broad in order to encompass the wide-ranging behaviour that it targets, he said. Professor O'Leary said while the term "grooming" was still being defined, a key factor was that adults always had control over their relationships with children, he said.

"Children may act inappropriately towards adults sometimes," he said. "An adult opportunist would see that as an invitation." A life is changed Nathan, meanwhile, claims he is the victim of a false accusation that has ruined his life. (The family declined to comment on this story.) He is heavily medicated for depression and anxiety. His girlfriend left him. Friends disappeared. "Everyone just made assumptions," he said.

Despite the acquittal, the Victorian Education Department refuses to lift a ban on him teaching in state schools. A spokesman said they must act on child safety allegations "regardless of any criminal proceedings". Bankrupt and back living with his mother, the former teacher now washes cars on minimum wage. But he is fighting to clear his name. He has lodged complaints about the police's handling of his case, contested the department's decision, and he is rallying politicians to change the grooming law, which he claims paints well-meaning adults as monsters. He believes in the need for the law, but says the wording is too broad. When asked if he thought he had an inappropriate relationship with Jack, he said: "I made it as public as possible and got the consent of the mother... so there wasn't really the alarm bells.

"I was probably very naive about that, but you have a kid who is changing for the better, do you leave that behind as a result of what someone may be thinking, or do you continue doing it if you see progress? I made the decision to keep working with him." *Names have been changed.