Bilingual schools split teaching time between two languages, with the split varying from 50-50 through to 80-20. Strong bilingual delivery requires consistent native-speaker teaching in both languages, integrated curriculum, and exit outcomes in both. Weak bilingual delivery is one language with the other taught as a subject. See 50-50 versus 90-10 bilingual models.
What bilingual really means
Bilingual schools split teaching time between two languages, with the split varying from 50-50 through to 80-20. Strong bilingual delivery requires consistent native-speaker teaching in both languages, integrated curriculum, and exit outcomes in both. Weak bilingual delivery is one language with the other taught as a subject. See 50-50 versus 90-10 bilingual models.
Europe
Germany-located bilingual schools (Munich International, Frankfurt International, Berlin Brandenburg) deliver English-German credibly. Spain has strong English-Spanish bilingual schools (King's College, Hastings School, British Council School). France has English-French bilinguals across Paris.
Asia
Singapore's bilingual schools deliver English-Mandarin at multiple credible levels. Hong Kong's ESF schools and Mandarin-immersion bilingual schools (Yew Chung, ISF Academy) are similarly strong. Beijing has mainland Mandarin-immersion options.
How to judge
Ask the school for exit data in both languages. A child leaving Year 11 from a credible bilingual school should be functionally bilingual with examinable outcomes in both. Anything thinner is one language with embellishments.
Related
See bilingual curriculum at international schools and bilingual versus international school.