Children at Blackmoor Park Junior School, in Liverpool, are eligible for a special school trip if they attend 100% of school over one term.
One pupil, with Type 1 Diabetes, was banned from going on the school trip because a hospital appointment stunted her otherwise perfect record.
Medical appointments are not exempt from the schools attendance policies, meaning Olivia Harkins, 7, will miss out because she had to see her consultant at Adler Hey Children's Hospital.
The young girls mother, Liz, accused the school of discrimination and said Olivia was devastated.
Liz, 47, said: 'It was her first clinic on Thursday since she moved to junior school and it only runs during school hours. We don' get a say in what time she has to go, we just get a letter with Olivia's appointment time. Even if she had the first appointment of the day, it would still be during school time.'
She continued, 'The school sent out the letter about the cinema trip last week and, at first, I didn't really pay that much attention. I thought it probably wasn't going to reply to Olivia - when I spoke to the teachers and found out it did, I was absolutely gobsmacked. They are discriminating against children who are sick.'
Olivia was diagnosed with Type 1 Diabetes in February after falling ill during the half-term break. She spent a week in hospital and now has to have insulin injections eight times a day.
Liz says that Olivia is still adjusting to life with the condition and wears a monitor to check her blood sugar levels, and has to prick her fingers several times a day to ensure her levels are stable.
However, Liz says that her daughter was still determined to make it to school, 'Olivia is devastated she's going to miss out on this trip. She's never off school and they know she has Diabetes.'
Mrs Harkins further adds: 'I can appreciate they want to get attendance up but why penalise kids who are genuinely ill? It's not a dentist appointment - it's completely different. Diabetes is a serious condition.'
Mrs Harkins husband has made a formal complaint with the school.