This sentence is from IELTS-teacher Youtube video (time 19:01):
A very important aspect of teaching is the ability of the teacher to shape their teaching style to the needs of their students.
My question is why one teacher shapes "their teaching style to the needs of their students".
If it should be teachers, this YouTube teacher is unreliable. We expect from a teacher to be perfect at this pretty simple English level. And if the sentence is OK, please explain to me why.