What you hear from some of your friends is actually a very widespread misconception among many Jews. Some 30 years ago I saw a study which was done by a Jewish sociologist to understand why Chanukah is perhaps the most widely observed Jewish holiday. He found it was because many Jews wanted to feel they, too, have a holiday during holiday season. Although I have some issues with his findings as to the main reason Chanukah is so well observed, there is certainly much truth to his findings, as you are experiencing in school.
The obvious fallacy in this reasoning becomes clear with the most cursory glance at the history of the two holidays. Chanukah was enacted in the year 138 BCE, upon the miraculous defeat of the Syrian Greeks and restoration of the Temple in Jerusalem. Christmas, as it is observed today on Dec. 25, was enacted by a Roman bishop in the year 350 CE. This is nearly 500 years after the Jews were already observing Chanukah!
I have always felt the fact that many Jews observe Chanukah to have a “Jewish Christmas” is one of the greatest ironies of our history. Many years ago I read the results of a study done by an Israeli historian which concludes that Christmas, as it is observed today, was initially established in December because that was the time the Jews observed Chanukah. Much like “Jews for Jesus,” early Christianity made great efforts to proselytize as many Jews as possible. They, therefore, attempted to make Christmas feel as Jewish as possible, partly by choosing the same time of year to celebrate. This, according to that study, is where their custom originated of lighting lights outside their houses, as the Jews used to light the Chanukah lights outside their homes in glass boxes (as many still do in Israel today). They picked Dec. 25 because Chanukah falls on the 25th day of Kislev. They enacted 12 days of Christmas, as the Torah reading on Chanukah covers the 12 days of the consecration of the Tabernacle in the desert. They even, (much later), added a man with a long white beard, to coincide with our celebration of the great sage Judah the Maccabee.
How ironic is it that Jews should keep our holiday to imitate theirs, when theirs was an imitation of ours to begin with!
I hope you can help your friends to join a Torah study group, so they can grow in their knowledge and pride of what it really means to be a Jew.
A joyous and meaningful Chanukah to you, your friends, and all the readers.
Rabbi Yerachmiel Fried