We have where each class chooses a song that they learn the previous week from eg Sing Up songbank. They practise it and then sing it in assembly on the following monday to the whole school. On all following assemblies of that week the whole school then join in. Then it is another class's turn the following week. It means that the children have some ownership of the songs. Usually the teacher chooses a couple or three of songs that the class can select one from. The Sing Up songbank has the lyrics for a whiteboard or to print off and backing track and has a huge range of styles/types of songs, some great fun and catchy, plus some more trad ones.