Laravel relationships setup

I'm working on a Laravel installation where I have (among other things)

• Teachers (table:users (cols: id, name, type), model:User, users.type = 2)
• Students (table:users (id, name, type), model:User, users.type = 1)
• Schools (table:schools (id, name), model:School)
• Collections of students (table:student_collection (id, name), model:StudentCollection)
• & table students_collections (id, user_id, collection_id)

I have managed to setup some relationships, but can't get my head around to get

• Which teachers teach a student
• Which collections does a student belong to

Currently I'm trying to get the collections with

//User.php
public function collections() {
    return $this->belongsToMany('\App\StudentCollection', 'student_collections_users', 'collection_id', 'user_id');
}

but it returns an empty result.

I'm using Laravel 5.3.

via Chebli Mohamed