As of now Laravel Schema Builder does not support SET datatype for columns. So, here is an alternative solution until someone add those code to Laravel.

Step 1: Create the table, use ENUM instead of SET.

Schema::create('schools', function($table)
{
    $table->increments('id');
    $table->char('id_number', 6);
    $table->string('school_name');
    $table->enum('level', array('Preschool', 'Kindergarten', 'Primary', 'Secondary'))->index();	// *** fix this
    $table->string('phone');
    $table->string('email');
    $table->string('location');
    $table->smallInteger('city')->unsigned()->index();
    $table->smallInteger('country')->unsigned()->index();
    $table->smallInteger('head_teacher')->unsigned()->index();
    $table->smallInteger('director')->unsigned()->index();
    $table->smallInteger('created_by')->unsigned();
    $table->smallInteger('modified_by')->unsigned();
    $table->timestamps();
});

Now change ENUM to SET.

$table_prefix = DB::getTablePrefix();
DB::statement("ALTER TABLE `" . $table_prefix . "schools` CHANGE `level` `level` SET('Preschool','Kindergarten','Primary','Secondary');");

If you have a better solution, then please let me know.