Data sources: prep→senior from each school's published Leavers' Destinations page (auto-scraped + manually curated). senior→uni currently modelled from each senior school's published Oxbridge % plus typical UK independent school distribution — will be replaced with school-by-school scraped UCAS data as scrapers progress. Multi-step P(uni|prep) = Σ_senior P(senior|prep) × P(uni|senior). Rows with low confidence are still shown but flagged.