CodeIgniter - Call method inside a model?

I have the following code:

class Badge extends CI_Model
{
    public function foo()
    {
        echo $this->bar('world');
    }

    public function bar($word)
    {
        return $word;
    }
}

But it always gives me an error on the line where echo $this->bar('world'); is.

Call to undefined method (......)

Your not loading your model inside your controller:

public function test()
{
    $this->load->model('badge');
    $this->badge->foo();
}

Because the code works - I've just tested it by pasting using your model unedited:

class Badge extends CI_Model
{
    public function foo()
    {
        echo $this->bar('world');
    }

    public function bar($word)
    {
        return $word;
    }
}

output:

world