As applications to build thousands of new homes crowd the desks of planning boards in our rural towns, planners and citizens alike are beginning the tricky task of estimating how much these subdivisions are likely to raise our property taxes to pay for the new schools, roads and other public services their future residents would require.

Much of the debate over forecasting the impact of development on our taxes can be boiled down to a single number: how many children from each of the new proposed homes will enroll in our public schools. With school taxes accounting for more than two-thirds of most property tax bills, and with ample evidence that each new home contributes far less in tax revenues than it absorbs in costly public services, the number of additional school students per newly built home-- the “enrollment ratio--” is one of the keys to predicting the financial impact of development.

How the enrollment ratio is calculated, and on what key assumptions it is based, should be the focus of great attention by our town planning officials as they review the onslaught of new subdivisions now before them.

For example, there are currently three different “fiscal impact” studies making their way to the Pine Plains Town Planning Board, where developers have proposed doubling the town’s current housing stock of some 1,200 homes. These studies typically base their enrollment forecasts on the flawed assumption that the families moving into new subdivisions in a predominantly rural setting will mirror the population profile of the people now living in crowded suburbs to the south.

The most defective approach to forecasting enrollment ratios can be found in what the Durst Organization has introduced to support its proposal for 951 new building lots on the former Carvel estate that straddles the towns of Pine Plains and Milan in northern Dutchess County. In their preliminary Environmental Impact Statement (EIS), Durst’s consultants claim that the demographic composition of the Carvel development, if it is inhabited by full-time residents, will mirror the combined population traits of three suburban counties: Dutchess, Putnam and Westchester.

Drawing on 2000 U.S. Census data for the three counties, Durst estimates that 22% of the homes will be owned by people older than 65, that only 34% of the Carvel homeowners will have school-aged children, and that the additional enrollment in the Pine Plains school district, which now educates 1,400 students, would be 399 new kids, or roughly 0.4 students for each of the 951 new houses.

Under Durst’s spurious logic of mirroring multi-county averages, we would also expect 12% of Carvel’s future residents to be African-American, another 20% to speak a foreign language at home, 4% to have mental disabilities and about 7% to be illegal immigrants, according to U.S. Census data on the three counties in question. (Durst’s representatives have refused to comment on the details of their study until an official period of public comment begins later this year.)

A second study, commissioned by the Pine Plains Central School District, uses the same three-county starting point as Durst, but it assumes that almost all of the 951 houses will attract families with school-aged children. The Carvel development, according to this report, would send 634 new students to the school district, an enrollment ratio of about 0.7.

A third analysis is also underway, sponsored by Pine Plains United, a citizens’ group concerned about the financial and environmental damage to the region from large-scale development. It is not clear whether this study, due for release in the spring, will use a similar multi-county averaging to estimate enrollment or whether it will adopt a method that many seasoned planners claim may be more reliable.

This method acknowledges that people who move to new homes in rural school districts tend, on average, to have very different demographic traits from the city and suburban neighbors they chose to leave behind. By tracking historic enrollment ratios from school districts that have experienced rapid residential development, this approach may provide a more revealing estimate of the trends that schools in our region can expect in the coming years.

Research conducted by this columnist on the Arlington School District, just 20 miles south of Pine Plains, indicates that during a housing boom that swept through the district in the mid-1990s the enrollment ratio was 1.3 students for each new house built, a much higher figure than multi-county averaging methods suggest. (For details, see the "Views From Gallatin" column entitled Lessons From Our Neighbors.)

Relatively small variations in the enrollment ratio can have a huge influence on our future property taxes. An analysis of various school districts in our region suggests that if the Arlington trends repeat themselves in Pine Plains, annual school taxes for existing property owners will rise by more than $10 million once the Carvel build out is complete. If the enrollment ratio at Carvel is only 0.7, the additional costs which current taxpayers will have to bear would be about $3 million each year.

“We should not be focused only on the number itself, which is hard to predict,” said Pine Plains School Board member Henry Boehringer. “We should be focused on how best to protect the school district from being overwhelmed by an influx of new students by making sure we have the staff and the facilities to meet their needs before our towns create too many building lots.”

With so many variables involved in predicting demographic trends and their effects on our taxes, town officials would be wise to take Mr. Boehringer’s comments to heart and consider various ways to slow down the pace of growth so they can monitor its fiscal impact before issuing blanket approvals that cannot be reversed. (One promising approach to phasing in growth is detailed in the "Views From Gallatin" column entitled The Pace of Growth.)