Schools in Antananarivo

http://www.egd.mg/    you can seek info from Nosybe at the facebook page
https://www.facebook.com/afnosybe/

If you speak English there is also the American School

https://asamadagascar.org/

It is expensive but the best advantage since English is most spoken Language in the world, French is down around 8th and is limited to a few countries mostly Africa where progress is a couple of generations away.   I am encouraging my daughters to learn Chinese, the next widely spoken language but mostly in China and a few other countries. 

you might consider schools in Mauritius

Hi! Thanks you for your input. The American  school  is a bit too expensive for me.  My daughter prefers to speak French and she is in a french school at the moment. There must be other alterative for French schooling in Tana.

You may already be aware of this but you may want to post your question on Facebook
Expat Madagascar.  I am also interested in your answers because by girls will be ready for higher education in about 2 years and not found in Mahajanga, as they go to college French.  I too cannot afford the English school.  I am looking into Mauritius but this is a long shot as well.