well, its not like you'll be inviting them to a party or something

westerners, in specific, unlike arabs or muslims in general, consider religion to be a very personal and private aspect that it is offensive to tell them what to believe or discuss it

I suggest you first try to be freinds with them, try to be close to them as a person they like and listen to, not like a student

then , indirectly, present some of Islams practices, like for example, take them to a tour in the great mosque in Athaiba (cuz i think its the only that has tours in it!!!)i

or for example invite them for a f6oor (in ramadhan of course) in your house

Dont lecture them or *tell* them what to think, let them ask the questinos themselves, if they are inetersted they will ask, if not, then dont bring the subject up yourself
And just respect them for that

It takes a while for a person to understand a new subject, let alone a new and different religion