Sign up for Weekday J and get the latest on what's happening in the Jewish Bay Area.

One of every five American Jewish schoolchildren is now enrolled in an all-day Jewish parochial school, according to a new "census" of Jewish day schools.

The enrollment figures — 184,333 students total, up a brisk 15 percent in the last decade — are being hailed far and wide as evidence that American Jews have finally taken day schools to heart.

Spurred by "frightening statistics" of intermarriage, Jewish leaders have seized on day schools "as a centerpiece of the communal strategy to promote Jewish identity and ensure Jewish continuity," census author Marvin Schick reports approvingly. The New York-based Avi Chai Foundation, a major force in the campaign, sponsored the census to help move things forward.

The actual numbers, awkwardly enough, suggest they're all barking up the wrong tree.

Examined up close, what the census shows is not a day-school system reaching out to growing numbers of uncommitted Jews.

No, the great majority of day schools are more like fortresses, where the most committed Jews wall themselves off from the society around — including most of their fellow Jews. Barely two-fifths of all day schools even try enrolling less-committed Jews. The numbers they reach are tiny, virtually meaningless in relation to the overall Jewish population.

In plain numbers, the census shows that about 75 percent of all day-school students, some 138,000, come from Orthodox families. The remaining 25 percent, about 47,000 students, come from non-Orthodox homes. Except for a small fraction crossing over in each direction, the two groups attend separate schools. Most Orthodox schools are effectively closed to non-Orthodox students.

Put differently, virtually all school-age Orthodox Jewish children in America attend day schools, but barely 5 percent of non-Orthodox Jewish children do. And that 5 percent appears in the main to represent the most Jewishly committed fraction of non-Orthodox families.

Youngsters from marginally affiliated homes, who might be seen as benefitting from the schools' outreach potential — as opposed to those enrolled because of already-strong family commitments — number at most 15,000 to 20,000. That's 1.5 to 2 percent of the total school-age Jewish population.

This is the situation at the end of 10 years of unprecedented growth in day-school enrollment and new school construction, at a cost of tens of millions of dollars. It's not pretty.

Schick, the census' author, is a respected educational consultant and lay president of New York's oldest day school, the Rabbi Jacob Joseph Schools. He compiled the census by contacting schools directly and requesting enrollment information for ages 4 and up.

All told, 676 schools were contacted. Schick says cooperation was "100 percent." Allowing for a handful of schools that may have gone unnoticed, it appears his figures present a nearly precise count, not an estimate, of the day-school population.

"They were very scrupulous in hunting down schools no one was aware of," says Leora Isaacs, research director of the mainstream Jewish Education Service of North America. "And they were appropriately cautious in interpreting the numbers that were given to them."

One of the census' biggest shocks is its depiction of Orthodox Jewry.

For one thing, they're much more numerous than commonly thought. The 1990 National Jewish Population Survey reported Orthodox Jews to be 6 percent of the total Jewish population, some 330,000 souls. But the 138,000 Orthodox schoolchildren in the census point to a much bigger population.

After factoring in statistics on family size provided by the schools, Schick estimates 500,000 to 550,000 Orthodox Jews live in the United States. That's 8 to 10 percent of the overall Jewish community. The Orthodox proportion of the school-age Jewish population is 14 percent, thanks to higher birthrates.

More startling, the census indicates only one-third of Orthodox students are enrolled in modern or "centrist" Orthodox schools — those that encourage college education and, in Schick's words, "evince a more positive attitude toward Israel."

The other two-thirds of the Orthodox student population — some 92,000, fully half the total day-school population — are enrolled in Chassidic and "yeshiva-world" institutions. These are schools where secular studies are downplayed and Judaic studies are commonly taught in Yiddish. They also report averages of seven children per family.

The biggest and most insular Chassidic stream, the militantly anti-Zionist Satmar sect, accounts for about 17,000 students, or 9 percent of the total day-school population. That's roughly the same size as the nationwide Solomon Schechter school system of Conservative Judaism.

The bottom line is sobering. For all the talk of day schools as a leading weapon in fighting assimilation, they're hardly even present on the battlefield. Right now they serve almost exclusively to educate children least at risk of assimilation. The vast population of at-risk Jewish youth — three-quarters of a million children from moderately affiliated families — isn't enrolled and won't be anytime soon.

What would it take to bring day schooling to the mainstream? It's hard to imagine. Even a modest doubling of non-Orthodox enrollment, to 10 percent, would require billions of dollars to build new classrooms, endow scholarships and train new teachers — assuming teachers could be found at current salary levels. Few knowledgeable observers believe sums like that are remotely available.

More important, the day-school mystique overlooks a crucial fact about intermarriage.

Several studies in recent years have shown convincingly that Jewish marriage patterns follow adolescent experience. More than anything, the studies show, whom Jews marry depends on whom they date. Jewish experiences during high school — Hebrew High, youth group, summer camp, Israel trips — are actually more effective in deterring intermarriage than a day-school education ending with eighth grade. And very few non-Orthodox high schools exist.

Building new Jewish day-high schools would help. But building enough of them would almost be impossible.

Non-Orthodox high schools currently have a combined enrollment of 2,200 nationwide. That's less than 1 percent of all non-Orthodox teens. Boosting it to 10 percent would cost at least $2 billion just for construction.

By contrast, the Zionist youth group Young Judaea currently reaches 12,000 youngsters a year at a cost of $20 million. It surveyed its alumni last year and found their intermarriage rate was just 5 percent.

Day schools aren't the same as summer trips, of course. They create an informed, educated Jewish population, steeped in the tradition in a way that youth groups can't match.

But that's a different discussion. You can't scare Jews with ignorance.