I often give da'wah to non-Muslims. However, my dawah is not to convert them to Islam, but only to make them know the truth about Islam and Muslims. In example, I explain them that it's not true if in Islam women are oppresed, it's not true if Islam suggest violence, etc. If then they want to convert to Islam, InshaAllah I will teach them about ibadah and other Islamic matters. But if they do not want to convert to Islam, it's OK. As long as they have know the truth about Islam, I am happy.
Just like you, I studied in Catholic elementary school since grade 1 until grade 4 before I moved to Bandung. All of my teachers there are female, they are nuns.
They're good teachers. They often went out in the evening, walked, not rode any vehicle only to visit their students homes. Sometime they visited my home too. They really care on me, they really love me. They taught me every thing except one, ... their religion.
Let me say honestly, they never tried to convert me or anyone to their religion, altought they had chances for it. Maybe this is the factor that makes me always respect to other religions.
I hope missionaries from other religions follow what I do. Give "da'wah" not to convert anyone but only to make other people know about their religions and build a religious tolerance.