I'm stymied by 18ac. H for "Headmaster" and "Headmistress", but not at Harrow. I have ?U?? P?S??
Can the second word be Posts. All I know about Harrow is they're said to pronounce their R"s like W's. I'm really curious about this answer. And is 20d Athena? If so, why exactly, and will that make 18ac have something to do with Pasta?