Disable text tab on WordPress text-editor

For disabling the text tab for all users except administrators, you can add the following:

function my_editor_settings($settings) {
    if ( ! current_user_can('administrator') ) {
        $settings['quicktags'] = false;
        return $settings;
    } else {
        $settings['quicktags'] = true;
        return $settings;
    }
}

add_filter('wp_editor_settings', 'my_editor_settings');