DES MOINES, Iowa (AP) _ U.S. Census data show Iowa has been spending less than the national average on students in its public schools. Iowa's per-pupil expenditure was nearly $9,800 per student, compared with the U.S. average of just over $10,600. District of Columbia public schools spent the most money: nearly $18,700 per pupil. Utah spent the least, at just over $6,060 per student.  Iowa spending has increased over the years, however. Iowa Department of Education data show the state spent more than $5,100 per student in the 1997-98 school year.