Question

students learn their lessons in class.In class teachers teach them. .

Student sit in the classroom[listening] to the teacher. 为什么用listening

Answer 1

students learn their lessons in class.In class teachers teach them. .
Student sit in the classroom[listening] to the teacher. 为什么用listening

因为listening是【现在分词】，listening to the teacher在此是【现在分词短语】做【伴随状语】。即：listening是伴随sit这一动作同时发生的动作。

Answer 2

现在分词做伴随状语，学生们坐着的同时在listening。