Disable WordPress dashboard for all but administrators.

function disable_dashboard() {
    if (!is_user_logged_in()) {
        return null;
    }
    if ( is_admin() && !defined('DOING_AJAX') && current_user_can('subscriber')) {
        wp_redirect(home_url());
        exit;
  } 
}
add_action('admin_init', 'disable_dashboard');