The star has admitted that she was once suspended for chatting up boys.
The mum-of-one was revisiting her primary school of Presentation Thurles as part of the upcoming Christmas Day edition of School Around The Corner.
Una (31) reminisced about her school days with old friends and laughed about getting sent home after being so flirtatious.
"Remember we got suspended for talking to boys at the school gate?" she said. "It was a build-up of a number of things where they were like, that's it, that's the final straw. I got a few blue cards at the time and the red card, that was it."
The trip down memory lane proved to be an emotional one for Una, who was overwhelmed by the experience.
Wandering the corridors, a teary-eyed Una commented: "I haven't been here since 1994, it a lifetime ago. I'm just so overwhelmed. A couple of my old teachers were there. It's just so nice that they turned up to see me."
Una says she loved the trip down memory lane. "I'm so proud of my school. I'm definitely a Tipp girl at heart and I'll cherish these memories from today."
School Around The Corner airs on Christmas day at 7:45pm on RTE 1