Few weeks back in witnessed a sing and dance competition on mathematical concepts. Wow! That was my first reaction since I had the general impression that Mathematics with all the computing it entails is by nature boring. Boy was I wrong! 
It is irrefutable that when the teaching process is fun and more interactive better retention is assured. So it's safe to say that no concept is too complicated if it was presented in an interesting manner that kids can relate to. 
My guess is the ability of songs to be chunked into rythmic repetitive lyrics makes retention far more effective than the usual memorization. Various learners are catered with this methodology as its multisensory task. 
Standalone a lecture on fraction would easily be forgotten by an average student but not when learners rememebr their colorful costumes and their gleeful chants or synchronous dance moves 