Update
You can make use of the add_rewrite_endpoint
:
add_rewrite_endpoint( 'schools', EP_PERMALINK | EP_PAGES );
You can then check in the sidebar for the schools
variable:
global $wp_query;
if ( isset( $wp_query->query_vars['schools'] ) ) {
// ...
}
What is worth mentioning is that your URL will look like www.example.com/performance/name-of-performance/schools/
instead of having schools
immediately after the custom post type’s name.