It is good to join the choral speaking as it can improve a lot on the sound management and improve the skill on solo speaking too.
Also, it is only for the 1st term, the competition would be no later than mid December.
So, if the teachers can allow them to wait each other after school, they can go back to home together after the training. But, they need to do some homework during waiting.
However, if the kids feel too tired to join the training after school, you have no choice but need to give up.