retrieve data from three tables

do you have primary keys on classroom and student?

if you want to find students of teacher you need a teacher_id column on the student, or, if students have many teachers then you will need a student_teacher pivot table

@Snapey yes i have pivot table between students and classrooms

I am assuming you want to get a Teacher's students based on the ClassRoom Model.

You will need to add a classroom_student pivot table which will allow you to get all the students in a classroom.

class ClassRoom extends Model
{
    

    public function students()
    {
        return $this->belongsToMany(Student::class);
    }
    
    public function teacher()
    {
        return $this->belongsTo(Teacher::class);
    }

}

class Teacher extends Model
{

    public function classrooms()
    {
        return $this->hasMany(ClassRoom::class);
    }
    
    public function students()
    {
        $classrooms = $this->classrooms;
        $students = $classrooms->flatMap(function($classroom){
            return $classroom->students;
        });

        return $students;
    }

}

It would probably look something like that

@spodlogar thank you for your very good answer worked for me