The headteacher at a Northampton school has pulled an ICT course after its GCSE cohort were all marked down.
Malcolm Arnold Academy said the Government changed the "accountability measures" for an ICT course its pupils were originally on this year.
As a result, the pupils' grades would not count towards their final qualifications.
The school then had to make a "rapid choice" between two similar style courses to replace the former course but teachers were unaware the new course they had chosen only held A-C grades.
Any grade achieved by a pupil below a grade C would be marked as a U automatically.
A letter from the school, which was shown to the Chronicle & Echo, read: "The moderation of the marking of the work was not rigorous enough and the teachers were not familiar with the course.
"This led to generous marking of the work undertaken, which was picked up by the external moderator who marked the whole cohort down as a result.
"The moderated grades were a fair representation of the sample, as several students hadn't finished their folders and therefore couldn't achieve the higher marks."
Reportedly 116 students took the course, which was made up of 75 per cent coursework and 25 per cent exam.
The school has appealed the examiner's decision but it was upheld by examining body, Pearson.
The letter continues: "We are very sorry for the upset caused. We appreciate that this may have had serious consequences for some students and we unreservedly apologise.
"Please be reassured that we have put steps in place to ensure that this can never happen again, including a decision not to run that course in the future."
The school has said it will pay for resit costs but one parent has said it is unrealistic to expect the children to have the time to take it again.
The parent, who wished to remain anonymous, said: "My child and several of their friends received outstanding results in other exams but had to collect their results, with ICT ungraded.
"That grade would have made a big deal for some students who did not do as well and needed to rely on it."
A Pearson spokeswoman said: “We are aware that this centre experienced some challenges in this summer’s examination series.
"We supported them during that time and continue to help them in working with their students going forward.”
Helena Brothwell who is an Executive Principal at Malcolm Arnold Academy told the Chronicle & Echo: “All parents have been informed of the outcome and their child’s results by letter last week and we are working closely with parents to support them.
"I am meeting any parents who have requested meetings and have replied to all correspondence received.”