In 1994, St. Catherine’s took on many new students when two nearby Catholic schools, the St. Vincent de Paul and St. Boniface schools in Elmont, closed.

The closings are part of a Long Island-wide and nationwide trend. According to Sean Dolan, a spokesman for the diocese, enrollment in diocesan grammar schools has dropped 34 percent in the past decade — from 28,709 in the 2000-01 school year to 19,261 in 2010-11. St. Catherine’s enrollment has plummeted by 53 percent over that time.

Dolan said he believes several factors are responsible for the declining enrollment on Long Island — which, he added, is a problem for public schools as well. One likely catalyst, he said, is changing Long Island demographics. The number of young parents with school-aged children who are staying on or moving to Long Island has dropped over the past decade, he explained, adding that according to diocesan officials, Long Island’s grammar-school-age population is predicted to drop another 7.5 percent by 2015.

Higher school and property taxes, as well as increasing tuition rates at Catholic schools, have also contributed to declining enrollment, Dolan said. In 2007-08, annual tuition for an in-parish student at St. Catherine’s was $4,400; for 2011-12, it’s $4,600. The Sacred Heart School in North Merrick saw an even greater hike over the same period, from $4,050 to $4,892. Costs are even higher for out-of-parish students.

“Public schools on Long Island are generally good,” Dolan said, “so if you’re a parent and paying a lot of taxes, you might decide to put your child in a public school.”