Class 'app\models\ not found in Laravel 5

I'm having a trouble using a model in a controller in Laravel 5.0. I created the model in a folder model under App. The code of the model id described as:

<?php namespace App\models;

      use Illuminate\Database\Eloquent\Model;

      class Observacion extends Model{

          protected $table = 'obs_usuarios';
          protected $fillable = ['observaciones', 'usuario_id','autor_id','tipo'];
}

Part of the code of the controller where I pretend to use it, is:

<?php namespace App\Http\Controllers;

use App\Http\Requests;
use App\Http\Controllers\Controller;
use App\models\Contrato;
use app\models\Observacion;
use App\models\Perfil;
use Illuminate\Http\Request;
use App\models\Configuracion;
use App\models\Usuario;
use App\models\Categ_profesores;
use Carbon\Carbon;
use Illuminate\Support\Facades\Input;
use Auth;
use Closure;
use Illuminate\Contracts\Auth\Guard;

class SecretariaController extends Controller {
    public function observacion($msg,$user_id,$autor_id,$type){
        $observacion = new Observacion();
        $observacion->observaciones=$msg;
        $observacion->usuario_id=$user_id;
        $observacion->autor_id=$autor_id;
        $observacion->tipo=$type;
        $observacion->save();
     }

I even made dump-autoload but I get this error:

FatalErrorException in SecretariaController.php line 155:
Class 'app\models\Observacion' not found

The line 155 is where I do: $observacion = new Observacion(); So, I don't know what else to check.

via Chebli Mohamed