Password-Lock a Single Page with PHP - How did I do?
A few things, mostly around logged_in:

private function check_login() {
    if (isset($_SESSION['logged_in'])) {
        // If logged in, take this action
        $this-&gt;logged_in = true;
    } else {
        // If not logged in, take this action
        $this-&gt;logged_in = false;
    }
}


Simply:

$this-&gt;logged_in = isset( $_SESSION['logged_in'] );


Also, the accessor method is_logged_in is being used quite well, yet there is a lack of a  corresponding set_logged_in. Add a set accessor, even if private, and use it exclusively.

Directly assigning the value of an instance variable in more than one place violates the DRY principle. That is, the assignment of $this-&gt;logged_in = &lt;&lt;value&gt;&gt; should exist only once: within the accessor. For example:

private function set_logged_in( $logged_in ) {
  $this-&gt;logged_in = $logged_in;
}


Once the accessor is in place, use it:

private function check_login() {
  $this-&gt;set_logged_in( isset($_SESSION['logged_in']) );
}


After the logged in status is using accessors exclusively, you can remove the logged_in variable completely and rely only on the $_SESSION['logged_in'] value. Think about what this implies for the check_login() method.

Next:

if ($pass !== 'TheChosenPassword') return false;

return true;


Simply:

return $pass === 'TheChosenPassword';