Bar mitzvah is one of the more misunderstood elements of modern
Judaism. While those in the
USA may have a good idea of what's involved, many people around the world confuse it with another male Jewish
rite of passage; the
bris. Yes, I've met a few people who believe that at thirteen years old, a Jewish boy stands up in front of his friends and family to have his
foreskin removed. Happily, this is not the case.
The bar mitzvah is essentially a modern innovation. The nearest scriptural source is in the Mishna.
Pirke Avot 5:25
He (Yehudah ben Teyma) would say: "A son of five years old for reading, twelve for Mishna, thirteen for Mitzvah, fifteen for Gemara, eighteen for Chupah, twenty to earn a living ...."
This passage was taken to mean that a male's legal responsibility began at age 13. After this time, he can sign contracts, make up a minyan (religious quorum), and generally start doing actions with real consequences.
Actually, the Halacha (Jewish law) doesn't merely use the age as a factor for adulthood, but also physical maturity. It's all in the pubes. There need to be at least three (I think) pubic hairs, with one on the left and one on the right. In some communities, the Rabbi will ask the boy if he fulfills the conditions, but (and I wonder why this is), that's pretty rare.
Bar mitzvah -- meaning son of the commandments -- happens automatically when a Jewish boy turns thirteen, by the Jewish calandar. Some people argue for the official time to be thirteen years and one day.
One of the new rights given to a bar mitzvah is being allowed to be given an Aliyah, or "called up", to the Torah. This means he is allowed to recite the blessings on the weekly reading in synagogue. For hundreds of years, a bar mitzvah boy would go along to the next Torah reading after he turned thirteen (on a Saturday, Monday or Thursday morning), ang get his Aliyah, and maybe a handshake afterwards.
Somewhere in the late nineteenth century it all started becoming a much bigger deal. Part of this trend probably came from an increasing secularisation among European and American Jews, and a related trend of poor Jewish education. There seemed to be a real communal need to have a rite of passage.
So the modern Bar Mitzvah was born. Children were encouraged not just to say the Torah blessings, but to read a bit from the scroll and maybe the Haftara too. The whole family was invited. It was seen as a way to at least teach boys Hebrew and some religious law. The United Synagogue in Great Britain requires boys to pass a "bar mitzvah test" before any ceremonies were allowed, as a way of forcing them to do some learning.
Of course, parties grew up for bar mitzvahs; after all, the family has come all the way from Chicago, and the Goldblooms threw such a good bash for their bar mitzvah. Quickly, the parties overshadowed the event itself and the modern bar mitzvah was born.
The US Reform movement argued that bar mitzvahs were counter-productive and too early. They experimented with a "confirmation" ceremony at the age of eighteen. It didn't really catch on, and where communities did introduce the practice, they kept the bar mitzvah anyway.
Today, bar mitzvah is a really big deal all over the Jewish world, with one exception; Israel. There, they tend give a child an Aliyah as soon as possible (even a Monday or Thursday morning), and just get it over with. There are always a lot of bar mitzvahs at the Western Wall in Jerusalem, but a lot of these are from abroad.
The ultra-Orthodox communities don't make that big a deal out of it either, though often it is from bar mitzvah that their boys start wearing black hats.