This work describes the results of speech intelligibility tests and measurements performed in primary school classrooms. The analyses were carried out in two laboratory-classrooms characterized by 1.6 s and 0.7 s occupied midfrequency reverberation time (RT), in presence of different types of noise. Speech babble and fan-coil noise were emitted into the room, traffic noise came from an external source and impact noise was generated on the floor upstairs the classroom. A total of about 3700 tests were submitted to 470 students from 7 to 11 year olds. The correlations between speech intelligibility and objective parameters are obtained for children of different age. The availability of data referred to two different conditions, with high and low RT respectively, allows to determine intelligibility decrease due to reverberation. A further research outcome is the effect on speech intelligibility of the different types of noise. One of the main finding of the work, as found in a previous research, is that younger children need more restrictive acoustical condition than older ones, for achieving the same level of speech intelligibility. A good correspondence was found between speech intelligibility and listening difficulty, the latter evaluated on a 5-point scale from "very easy" to "very difficult".