School superintendents blame lean budgets and cramped classrooms for the $2,000-plus tuition many charge for popular full-day kindergarten programs.

But a poll suggests the bell is tolling for a full day for 5-year-olds.

“The children that often most need it, those families can’t afford to pay it,” said Margaret Blood, director of the group Strategies for Children, which is sponsoring legislation on Beacon Hill asking for more funding.

Some families would rather ease their children into a school environment, she said, but her group conducted a poll that showed 81 percent of families believe kindergarten should be full-day.

Boston offers free full-day kindergarten, but many Bay State communities do not or charge a fee.

Only nine states mandate full-day kindergarten. In Massachusetts, the length of the kindergarten day is set by the district, leading to disparities.

“The first issue is we do not have space,” said Framingham Superintendent Christopher Martes.

Framingham has a lottery for parents who want full-day kindergarten, with the winners required to pay $2,500.

But, proponents say, there’s no argument a full day has its benefits.

“From an educational point of view, I think it certainly would benefit students to be in an instructional environment longer,” said Holliston Superintendent Bradford Jackson. His town charges tuition for full-day classes.