•First-graders benefit from SFAS regardless of classroom acoustics.•First-graders benefit from SFAS regardless of the level of language development.•SFAS increase speech perception in classrooms with short reverberation time.•SFAS decrease speech perception in classrooms with long reverberation time. The purpose of the study was to investigate in natural conditions the impact of sound field amplification systems (SFAS) on the perception of monosyllabic nonsense words in first to fourth-grade students with and without language disorders in classrooms with different acoustics. One hundred forty-five monolingual primary school pupils were included in the study. Two study groups were formed: pupils with typical language development (TD) (n = 145) and pupils with developmental language disorders (LD) (n = 72). Acoustic measurements were made in twelve classrooms with different reverberation time. Monosyllabic nonsense words perception tests, presented by an examiner, were carried out in classrooms with and without SFAS. The number of errors in the test carried out with SFAS in different acoustic conditions reduced in pupils of Grade 1 with TD (Z = –2.273, p = .023; Z = –1.965, p = .049) and with LD (Z = –2.410, p = .016; Z = –2.156, p = .031). The SFAS installed in large classrooms with long reverberation time significantly increased the number of errors in nonsense monosyllables perception (rS = 0.361, p < .01, rS = 0.229, p < .01). The mean number of errors in children with LD was higher than in children with TD in monosyllabic nonsense words tests carried out with and without SFAS (U = 3194, p < .001; U = 3518.5, p < .001). First-grade students benefit from sound field amplification in perception of monosyllabic nonsense words regardless of classrooms acoustics, and irrespective of the level of language development. The positive effect of SFAS on nonsense word perception was not observed in pupils of Grade 2, 3, and 4 of primary school. Classroom acoustics affects the expected positive impact of SFAS for children older than first graders. Amplification increases speech perception and decreases the number of errors in the reproduction of monosyllabic nonsense words in classrooms with short reverberation time.