On the face of it, the No. 1 idea outlined by the leaders of the Jewish Federations of North America in response to the challenges laid bare by the recent Pew survey of American Jews sounds like a great concept: free Jewish preschool for everyone.

What could be bad? Especially if you’re a parent paying $1,200 a month for your kid’s preschool.

But the more you think about the idea, about which Jewish Federations CEO Jerry Silverman and board chairman Michael Siegal offered just five sentences in an Op-Ed last week published in the Huffington Post and the Forward, the more questions arise about its viability and effectiveness.

When I called Silverman for more details, he acknowledged that the free-preschool idea (and the three other suggestions floated in their opinion piece)  fell short of being a detailed policy proposal. Instead, Silverman, now in his fifth year as CEO of Jewish Federations, said that he and Siegal were attempting to kick-start a much-needed conversation about how to respond to the issues underscored by the Pew survey.

“Right now, Uri, it’s an idea,” Silverman told me. “These are four concepts and ideas. You know? Our goal is to unpack these, take a look at these, take a look at the models that are already out there, and see what this idea could really turn into. And once we unpack it we will be able to really see what is reasonable and what is executable. But we think it’s in the right direction.”

So in the spirit of unpacking, let’s start with the biggest question of all: How much would the free-preschool idea cost? By any measure, the price would be staggering.

A study not long ago by Ilene Vogelstein found tuition for full-day Jewish preschool programs ranges from $6,000 to $20,000. Let’s split the difference and say we’re talking about $12,000 per year per kid on average.

Now, how many Jewish preschool-aged kids are there in America? The Pew survey estimates that there are 1.8 million children living in households with at least one Jewish adult. Of those, at least 1.3 million are being raised as Jewish in some way. I would assume the federations want to tackle the larger number, especially because it includes the least affiliated. But even if we take the smaller number and consider preschool a two-year endeavor, there are some 200,000 Jewish kids in America that would fit into this cohort. That’s about $2 billion per year. And even if we interpret Silverman and Siegal’s call as one freebie per family (they called for “offering free Jewish preschool to every Jewish family”), we’re still talking about $1 billion per year, given that the average American Jewish family has 1.9 kids.

Who’s going to pay for that? The authors don’t say.

Second, is free really the wisest strategy? Preschool differs in one significant way from almost all the other mechanisms — day school, Hebrew school, synagogue membership, etc. – heralded by Jewish engagement advocates. All those options require a special and significant financial commitment parents otherwise would not make. But most parents – Jewish or not – are paying for preschool or child care anyway. That’s one of the reasons the penetration rate for Jewish preschool is so high in some communities. (A 1999 study by demographer Ira Sheskin found penetration rates of 56 percent of all Jewish kids in Los Angeles, and 80 percent in Charlotte, N.C.)

So why strive to make Jewish preschool free when simply making it less expensive than the alternatives could go a long way toward attracting more families? A make-it-cheaper approach would dramatically reduce the price tag of any new preschool push and still have a major impact.

Third, is cost really the main impediment to higher enrollment? In my neighborhood, the main deterrent to Jewish preschool isn’t the money as much as the hours. Though I live in a vibrant Jewish community with plenty of synagogues and Jewish educational options, only one of the many Jewish preschools stays open after 3 p.m., and most offer less than three hours of programming per day – not a great framework for a family with two working parents. Perhaps that’s why a study in 2004-‘05 by New York’s Board of Jewish Education (now the Jewish Education Project) found only 3 percent of Jewish kids in New York were enrolled in Jewish preschool.

For others, the deterrent to Jewish preschool may be the curriculum. In a 2001 monograph for Avi Chai, Jewish educational expert Jack Wertheimer wrote that it is a “well-documented fact that many teachers in Jewish preschool programs, whether in JCCs, synagogues, or day schools, lack a strong Jewish education — and a significant percentage are not even Jewish.”

All this isn’t to say that getting more kids in Jewish preschools is a bad idea. As Vogelstein writes: “Early childhood Jewish education strengthens the Jewish identity and the Jewish ritual behaviors of parents and impacts parents’ future Jewish education decisions… These studies suggest communities, federations and philanthropists should ensure that all Jewish children have the opportunity to attend an early childhood Jewish education program.”

The question is how we get from here to there.