A primary school head teacher has warned parents that children found with e-cigarettes face being excluded.
There has been a "worrying" increase in the number of pupils caught with the devices at Lowerhouse Junior School in Burnley, said principal Claire Holgate.
In a letter to parents, she said it was "incredibly concerning" nicotine products had been found.
The letter says e-cigarettes put "staff at risk" and alleges nicotine use has been linked to memory impairment.
It warns that pupils found with e-cigarettes "will be dealt with in line with the school's behaviour policy", which could lead to exclusion.
In a statement to the BBC, Mrs Holgate said: "A letter was sent to parents to reinforce the message about the possible dangers of using e-cigarettes.
"We also wanted to make parents aware that we're doing what we can in school to discourage young people from smoking or vaping in any form, by providing some age-appropriate education to all our pupils about the potential dangers."
When asked why the school believed that nicotine use had been linked to memory impairment, it said Mrs Holgate had taken her research from the American Lung Association's website.
The association states that "nicotine use during adolescence and young adulthood has been associated with lasting cognitive and behavioral impairments, including effects on working memory and attention".
The school added that "there have been no incidents at school affecting staff".
The school, in Liverpool Road, was rated as "good" by Ofsted on its last inspection in June 2014.
In January 2013 the primary - which caters for pupils aged 7-11 - had been branded "inadequate".
Correction 26 June 2017: A sentence in this piece which questioned the head teacher's evidence for advising that nicotine use had been linked to memory impairment has been removed.