Parents have been told by a school head teacher to warn their children against urinating in the playground. Kay Church, of Hannah More Infants' School in Nailsea, north Somerset, wrote to parents addressing the matter of "toilet etiquette" in a newsletter.
Mrs Church said the "unacceptable behaviour" was "not at all representative" of the school.
However, she confirmed there had only been one such incident reported to her.
In the newsletter, Mrs Church wrote: "Sadly, it has been brought to my attention that at the end of the school day a small number of pupils are allowed by parents to urinate in the school playground.
"Clearly this is totally unacceptable behaviour particularly as all pupils and families know where the toilets are in school."
Chair of governors Ann Tonkin said there are "plenty" of toilets in the school building for children to use, and staff would be happy for pupils to return after lessons to use the facilities.
"If an adult were to behave in the same way in a public place there would be consequences," she explained.
"Parents need to ensure that they teach their children that it is not acceptable to urinate in a public place."
North Somerset Council said it was an issue which parents have been made aware of through the school newsletter, and did not wish to comment further.