WASHINGTON -- Schools are doing a better job of identifying students who are eligible for free or reduced-price school lunches, but some states are much better than others, the Agriculture Department says in a report to Congress.

In 2008-2009, 78 percent of schools identified eligible students by using government records of which households already receive aid like food stamps. Use of the so-called direct certification method, the most efficient way to enroll school children in subsidized lunch programs, was up 11 percentage points from the previous year, according to the report, which is being delivered to Congress on Tuesday. A copy was obtained by The Associated Press.

Direct certification helps eliminate the lengthy application process for free meals.

Despite the overall improvement, the report shows a wide disparity in performance from state to state. The top four states -- Alaska, Delaware, New York and Tennessee -- all directly enrolled more than 90 percent of students from households that receive food stamps.

The bottom four -- the District of Columbia, Idaho, Missouri and New Hampshire -- directly enrolled 50 percent or fewer students whose families received food stamps.

Agriculture Secretary Tom Vilsack said the report shows areas where states can improve.

Kevin Concannon, the USDA's undersecretary for food, nutrition and consumer services, said the report "will help us share promising lessons from the most successful states."

Schools that lag in efficiently enrolling kids in their lunch programs are disproportionately smaller and rural, the report concludes.

The school lunch program provides low-cost or free lunches to 31 million children each school day.