Pivot table with extra column and where condition

I'm working on school management system, I need to assign the student class and section here is the table structure.

Table: classes id, name

public function sections()
{
    return $this->belongsToMany('App\Section');
}

public function students()
{
    return $this->belongsToMany('App\Student');
}

Table: sections id, name

public function classes()
{
    return $this->belongsToMany('App\Class');
}

Pivot Table: class_section class_id section_id

Table: Session (Current academic year)

id, year (17-18)

Table: Student id, name

public function classes()
{
    return $this->belongsToMany('App\Class');
}

Now I have created a table: class_student with extra columns

class_student

class_id | student_id | section_id | session_id

1       3            2                   1

While I'm editing student I need to fetch the student details with current session_id.

How to write the query to check where condition in the pivot table for an extra column?

If is there any possibilities with eloquent please let me know.

Thank you.