Over the years, I've helped a number of Christian students organize Bible study groups. They can hold study meetings and prayer meetings (on school property), announce their activities in flyers and post them on school bulletin boards, etc. They can invite everybody, including non-Christians to come. As long as they follow the same rules as other extra-curricular groups, and do not disrupt classroom activities, it is entirely legal for them to do these things.
The Supreme Court has even ruled recently that OUTSIDE groups (not student led groups) can conduct evangelizing activities on public school property. I do not remember the name of the case, but if you go to Jay Sekulow's ACLJ site you can find this case and many others setting out how religious activities can legally be conducted on school grounds. Sekulow's group has been very active in making sure Christians are able to exercise their rights in the schools.
If the Muslims assert those rights, and follow the same rules, I don't see how you can prevent them from doing so. It's all very well to say that Christians wouldn't be able to evangelize in Pakistan, but isn't that why we live in the US, not Pakistan? If w e start saying, Christians (or Jews, or Mormons, or .... ) can do it, but not Muslims, then we might as well be living in a mirror image of Pakistan.