Singing encourages relaxation through deep breathing, getting more oxygen to the brain to keep children more focussed.
A singers brain handles many tasks simultaneously from remembering their cues, lyrics and where to take breaths during the course of a song.
"The foundation of reading is speech and to learn how to speak, children must first be able to distinguish speech from all other sounds. Music helps them do this." (Dr Anita Collins)
Singing songs encourages children to become the character in the song, to think about the emotion that's required to deliver the lyrics which in turn spark's their imagination - especially when they incorporate songwriting skills into their singing lessons.