A “technical mix-up” has been blamed on 30 primary seven pupils receiving the wrong results for their entrance test to the Rainey Endowed School in Magherafelt.
All the pupils have now been given the correct marks.
Principal Mark McCullough said up to six or seven pupils got lower marks in the second set of results.
“We will ensure those are addressed through the admissions process,” he said.
But Mr McCullough said the “vast majority” of the pupils who received incorrect scores had their marks increased.
One of the pupils whose marks were lowered was the son of Ulster Unionist MLA Sandra Overend.
“It has been a very distressing time,” she said. “Some got better results than they got first thing in the morning, and some got worse results.
“For those especially who got worse results, it’s heart-wrenching for them.”