Montgomery County Public Schools spent more on its pension program last year as teachers, principals and staff retired later to bring in more income. Fewer than one of four school employees retired when they became eligible for full pensions. Just 25 percent of 65-year-old employees chose to end their tenures, and once they passed that retirement benchmark, they became more likely to plug away into their 70s: 82 percent of school employees ages 66 to 67 kept working, along with 85 percent of those between 68 and 69.

“When we move into the 60s, [retirement] rates are lower than we saw before,” said Douglas Rowe, who headed the audit for consultant group Mercer.