我想入合唱團,但爸爸不讓我入

show your sincerity to your father, and tell him that ECA is important for a student and there are many opportunities for you to perform and build up a wider social circle and team spirit , also self-confidence

remember tell him that you will strike a balance on both acadamic and activities, and you better set up a time table and goal for yourself.

和爸爸商量你的心願,希望他能成全你，也找媽媽商量一下，讓媽媽幫忙。

study better have a good result tell him you can get good result even you join
school choir.
show him how you love singing and tell him that it will not destory your learning.

可以找媽媽商討，也可以說出參加合唱團的好處，例如可以學自立。