Multiple custom menus – getting the main menu to highlight correctly

I plan to use a single custom side menu for the 4 main menu items. If I go to http://www.robertkett.norfolk.sch.uk/index.php/school/ it shows the main menu item highlighted correctly, however if I go to a sub menu (via a different custom menu) http://www.robertkett.norfolk.sch.uk/index.php/school/welcome/ it does not highlight.

Any suggestions on a way around my problem?

(I’m using jquery-vertical-accordion-menu as the plugin/widget to display the custom menu)