First, you can listen to an audio answer of your question in this link www.soundcloud.com/rabbialonanava/can-a-teenage-boy-have-conversation-with-a-girl or you can listen to the recording at the bottom of the page.   As for you question, it is highly recommended for a boy over the age of 13 (Bar Mitzvah) to avoid any type of conversation with a girl over the age of 12 (Bat Mitzvah) even if it is a conversation about Torah, cause any type of conversation can lead to an unwanted action that will be prohibited by the Torah. Even a platonic relationship for the sake of promoting Torah is recommended to avoid for the same reason.   I am not aware what is a coe-ed Israel program (modern-orthodox) if you can share with me more info i will be more than happy to advise you. If you are under the age of 18 and your parents are responsible for your education, you can always share with them your desires and opinions and if you wish to go to a different program, they should know about it and possibly send you somewhere else Please let me know what are your interests and I will gladly help you come to the right decision Rabbi Alon Anava