The Lawrence public school district trimmed elementary class sizes by investing $2.3 million to hire more teachers over the past five years, officials said Monday.

Adding teachers to the payroll dropped average class sizes and diminished the number of “combination” classes, which result from mergers of two grades in one room.

The district’s average class size in kindergarten through third grade was 18.9 students when school started in August, down from 19.4 in August 1999.

An average of 21.2 students were in fourth- to sixth-grade classrooms, down from 22.9 students in 1999.

“The critical thing is that it is going down,” said Mary Rodriguez, the district’s personnel director.

The issue of class size surfaced at the school board’s meeting Monday at district headquarters, 110 McDonald Drive. The topic wasn’t on the board’s agenda.

Money to hire the extra teachers was drawn from the district’s general fund as well as from federal grants designed to slice class sizes. Of $2.3 million spent in Lawrence elementary schools, $1.1 million came from the district and $1.2 million came from federal sources.

The number of combination classrooms in the district has been cut from 25 in 1999 to two this year.

“We really have made gains to improve that,” said Supt. Randy Weseman.

During the five-year period summarized by Rodriguez, the district has cut millions of dollars in spending and raised student fees to balance its budget. The district also closed four elementary schools — Grant, Riverside, Centennial and East Heights.

In addition, enrollment of elementary students has fallen by a minimum of 120 students in each of the past four years.

Under district policy, the goal is to have class sizes in kindergarten to third grade ranging from 13 to 17 students. The goal in fourth through sixth grades is 26 or fewer students.