Flight Instructor flying C-152 aircraft discovered aircraft to be in un-airworthy condition during post flight review.

Narrative

I was instructing a student on his initial solo flight. Prior to flight; we checked the airplane out from the scheduling system; but I failed to notice the airplane was grounded due to a maintenance issue. We successfully completed the mission; but after the flight; I noticed the grounding annotation in the system. To my further embarrassment; I was the pilot who grounded the aircraft for this and another maintenance issue; but I thought both issues had been cleared by maintenance.I was also under the mistaken impression the software of the scheduling system would prohibit checking out a grounded aircraft. Further; the keys to the grounded aircraft were still available in the lock box.My failure to confirm the maintenance status of the airplane caused me to fly it in a non-airworthy status. It was a foolish mistake made in haste to get the mission completed; but it could have had serious consequences. I will redouble my efforts in the future and emphasize the point to my current and future students.