Cross Currents's Eytan Kobre has evidently been reading some of the recent blog discussion about the Bat Mitzvah celebration as an example of the 20th century adaptation by Orthodoxy to modern mores. There are a number of posekim who discuss the permissibility of the Bat Mitzvah, from the Seridei Esh to the Iggeros Moshe. Kobre is skeptical that Mordecai Kaplan really did "invent" the Bat Mitzvah (although he allows that Kaplan is the "dude who invented Reconstructionism (patent pending)").
How, you ask, do I know the bat mitzvah was Kaplan’s baby? Because, over the years, I must have read the same sentence in at least 5 or 6 different Jewish papers or books, and always with a sober air of authority (those familiar with the literature know that received wisdom of this sort about the Orthodox tends to get regurgitated repeatedly), in roughly these words: “Even the Orthodox have been influenced by the other movements to accomodate modernity*, as in their adoption of the bat mitzvah ceremony first performed by Mordecai Kaplan.” What a gas.To an extent I agree with Kobre. I don't think that Orthodox Jews who make Bat Mitzvah parties for their daughters are consciously influenced by Reconstructionism. But the Orthodox Bat Mitzvah was not created ex nihilo. It came from somewhere. Unless Kobre can provide a different, plausible point of origin, there is little reason to assume that the seeds of this idea wasn't initiated by Mordecai Kaplan in the 20th century. No one is saying that Orthodox Jews said "Hey, those Reconstructionists (patent pending) have a great idea. Let's make a party for our Chani when she turns 12 just as we made one for Shloimy when he became 13." Or at least I'm not saying it. Sometimes that is how influence works. It is overt. But it is likely-to-certain that this isn't the case here. What happened was that the Bat Mitzvah celebration was initiated by Mordecai Kaplan and the latent idea was released, as it were, into the atmosphere. Formerly a young lady's ascension to gedola-hood went marked primarily by fasting with the adults. Fast forward 60 or 70 years later and even in chareidi circles (although not in all) a young lady has the occasion marked by, if not a seudas mitzvah, then a party with her friends. This did not happen and probably would not have happened in the 14th century. It happened in the 20th century. Why? Because of external influences and pressures on Orthodox Jews to adapt to the reality that 12 year old girls cannot accept that their transition to halakhic maturity would go unnoticed while that of their brothers would be a communal celebration (to say nothing of a catered affair, another 20th century adaptation to something-or-other).
*In fact there are obvious examples of this, notably the patently-not-controversial-now idea of a rabbi addressing his congregation in the vernacular.