As it turns out, they were wrong.

This is the second year the city has been enrolling preschoolers through the grant program, and in neither year has it filled all 195 slots. And not because there aren’t eligible children.

Fuller estimates half of Springfield’s preschool-aged children are not enrolled in programs, and she admits that number could be off by as much as 10 percentage points—which speaks to a major barrier in preschool-expansion efforts. Communities largely don’t have a handle on the exact size of the population they’re trying to serve.

“It’s a huge challenge,” Fuller said. “It’s hard to believe that accurate data should be such a challenge. It’s almost unbelievable.”

Amy O’Leary, the director of the Early Education for All Campaign run out of the state advocacy group Strategies for Children, has seen this issue play out in community after community across Massachusetts. Nobody at the local level is in charge of collecting the data, leaving cities like Springfield struggling to cobble together as accurate a picture as possible.

Decennial data from the U.S. census provides the most accurate population counts, but local organizations can only learn so much from something already seven years out of date. Springfield has used the annual American Community Survey population estimates with help from a regional planning commission to identify the entire preschool-aged population. From there, people working on the expansion effort have identified the early-childhood centers in each neighborhood, calling one by one to find out their enrollment totals.

These sources provide only a snapshot of the service gaps, but one that can at least give Fuller and others a place to start. From there, it’s a matter of actually reaching those families to find out how best to serve them.

Communities can ignore the data gaps and jump right into preschool expansion, but they do so at their own peril. Parents make decisions about early childhood based on a variety of factors. Adding new classrooms to buildings that happen to have space, rather than buildings that are in communities with real demand, could lead to unfilled seats. Offering half-day preschool to families that need full-day accommodations likely won’t work. And alternatively, asking families to suddenly go from zero to eight hours of preschool may not be well-received in some circles either.

O’Leary has encouraged communities planning for preschool expansion—both with federal dollars as well as state grants—to start with a true needs assessment. And that means identifying the target population.

Strategies for Children filed its first bill for preschool expansion in 2002. Over the 15 years since, it has been clear to O’Leary that the gaps in understanding of the local landscape would become a problem. But without real money on the table to tackle planning, let alone preschool expansion, the gaps remained.