Six parents are being prosecuted for truancy every week in the Thames Valley area, amid a government crackdown on unauthorised school absences.
Councils covered by the Thames Valley police took 290 parents to court in 2017, figures released under the Freedom of Information Act show.
Of those charged, 220, or 76%, were found guilty.
Courts issued fines in 166 cases and handed out community sentences, such as an order to do unpaid work, on one occasion.
Prosecutions for truancy across England and Wales reached 18,377 during 2017 - 6,600 more than during 2013 - with parents being hit with more than 11,700 fines.
The National Education Union said fines were counterproductive, and that there was no easy fix for truancy
Dr Mary Bousted, joint general secretary of the NEU, said: "One thing that is certainly needed, to ensure pupils are in school and engaged in learning, is a dialogue between the school and parents or carer.
"Fines invariably have the complete opposite effect, creating unnecessary tensions between schools and families.
"Clearly this is counterproductive to getting the problem resolved.”
Seven in 10 prosecutions in the Thames Valley area were against women.
Women were also more likely to be found guilty - 81% of those prosecuted were convicted, compared to 65% of men prosecuted.
Sam Smethers, chief executive of women's rights charity Fawcett Society, said it was concerning to see mothers penalised more often than fathers, adding that society was "too quick to judge mothers".
Both parents have a legal obligation to ensure children attend school regularly, regardless of whether they are separated.
Headteachers and councils can also issue on-the-spot fines to parents for unauthorised absences instead of taking them to court, but may prosecute if the fine is not paid.
Around 400,000 such fines were issued in England and Wales between 2014-15 and 2016-2017.
A recent academic study found that parents of pupils with special educational needs and disabilities were frequently being prosecuted for truancy, when they would have benefited from more support.
Professor Rona Epstein, one of the researchers, said: "It's horrendous that these parents are prosecuted, and it's costing an absolute fortune from the public purse to do so."
She added that mothers were the sole parents prosecuted in many cases, even if the child belonged to a two-parent household.
In total, parents have been prosecuted for truancy 1,497 times in the Thames Valley area between 2013 and 2017.
The courts found them guilty in 1,127 cases, imposed 820 fines and handed out 19 community sentence.
A Department for Education spokesman said: "Evidence shows that every extra day of school missed can affect a pupil's chances of achieving good GCSEs, which has a lasting effect on their life chances.
"We are clear that pupils can only take term-time leave in exceptional circumstances, and where this leave has been authorised by the headteacher."