A mother found guilty of failing to ensure her son attended school despite trying to physically drag him there has had her conviction quashed.
The woman was convicted last year by Liverpool magistrates using the Education Act 1996.
A High Court judge ruled it should have been down to the prosecution to prove she had failed to secure his attendance at his Liverpool school.
Magistrates had wrongly "reversed the burden of proof", he said.
Mr Justice Collins heard that "Mrs P" had done her best to get her "large" 14-year-old son to school.
But he was adamant he was being bullied and refused to go, attending 23 out of 122 possible school sessions.
Magistrates had found her guilty on the basis she had not done everything she could have, suggesting she should have tried to get the help of the boy's father.
But Mr Justice Collins said on Wednesday there was no evidence to justify the conclusion that he would have been any help.
He said: "If the Justices had applied their minds to the matter in a proper fashion and had concluded - as they ought to have done - that the burden of proof remained on the prosecution, it seems to me they would have been bound to reach the conclusion that P was not guilty."
Mrs P's solicitor, Zoe Taxman, described the ruling as a signal to local education authorities not to prosecute parents who were doing their best with difficult children.
"We want to see fewer prosecutions of parents in the future and more help offered," she said.
A spokesman for the Department for Education and Skills said they did not believe the ruling should affect any future prosecutions.
He said there was "a significant package of investment and measures" to help support parents trying to tackle their children's truancy.
"But where parents are not unable, but simply unwilling, to fulfil their responsibilities, legal sanctions through prosecution or penalty notices should apply," he added.
After the hearing, Liverpool City Council said it took parents to court when all other avenues had been exhausted.
"Every lesson counts for pupils during their education and the law says it is the responsibility of parents to ensure they attend," a spokesman said.
"The city council's policy of using all available means to improve attainment remains unchanged."