Identical twins Aaron and Conor Daly from Rathcoole in Co Dublin had identical ambitions to study medicine.
They were both awarded the exact same calculated grades by their school, the maximum 625 points.
But the 18-year-olds ended up with different results.
Aaron was downgraded in two subjects which resulted in Conor getting a place in Medicine in UCD and Aaron missing out.
He is now studying his sixth choice, which was Bio Medicine in UCD.
Aaron told RTÉ Radio 1's 'Liveline' that he did not understand why he was penalised when his brother wasn't as they have had similar grades and performances since first year.
Their mother, Denise Daly said she was heartbroken when Aaron was downgraded and that it took away from what Conor had achieved.
"We weren't able to celebrate Conor because of what happened to Aaron. The day the grades came out I lost all faith in the system," she said.
However, Denise said the news today offered a glimmer of hope that Aaron might get the results he hoped for.
Aaron hasn't receive any contact from the Department of Education be he and thousands of other students will be anxiously waiting to hear if their grades are going to be changed.
The ASTI said it is shocked and disappointed by the errors.
ASTI President Anne Piggott said she was shocked that such a mistake could happen "at this level" and she said it has raised the question as to whether everything else had been done correctly or if there were more errors in the system.
The Union of Students in Ireland said the Minister said no one will be disadvantaged but that students need to know "how she will make that a reality".
USI President, Lorna Fitzpatrick said, "There are so many issues that have to be resolved. Fees have already been paid, rents for accommodation paid and many students have moved to towns or cities where they're attending college."
She also queried how more college places could be made available when students had been told that all the additional places that were possible had already been added.
Career Guidance expert Brian Mooney told RTÉ's Six One News that many more students could be upgraded.
He said the fact that the way Junior Cert results were used in the calculation of grades meant the collective performance went down "once you correct that you improve the performance of every class group in every subject in the entire the country".
Those wanting to sit the actual Leaving Cert exams in November had until this Friday to register to sit the exams.
But the National Association of Principals and Deputy principals says that deadline is no longer realistic and they want students to have more time to consider their options.