In recent years, several studies started to focus on the sound evaluation of classrooms, to verify the acoustic comfort. These assessments are the first?s steps of the development of strategies for improvement of classrooms comfort, aiming the enhancement of the learning process of pupils and providing good conditions for teaching. This study is investigating room acoustic descriptors with great importance in classroom acoustics, which are the Speech Transmission Index (STI), Sound Definition (D50) and Reverberation Time (RT). The investigated classrooms are located in two buildings from the Federal University of Paraná, one from the 1960s and another from 2016. In 2007, some of the classrooms in the old building had a new roof covering. The old material, with a good sound absorption material, was replaced by a PVC coating. To characterize the acoustic comfort, room acoustic measurements and simulations were performed, and the results were compared with existing standards ISO 9921:2003 related to STI and ANSI/ASA that rules the RT. The room acoustic descriptor D50 was evaluated according to recommendations from Fasold & Veres (2003). As expected, the new building presented classrooms with greater acoustic comfort. In the classrooms of the old building, the refurbishment of ceilings decreased their acoustic quality, as shown in the results of the comparison between measurements and simulations of classrooms, with original and refurbished ceilings. In short, this paper shows that the decision to replace the original room coverings with PVC resulted in a gross error.