Voters in the Indian River School District head to the polls today to weigh in on the district's referendum.   If approved, the proposed referendum will fund construction of new classroom space at six schools plus teachers and materials for those new classes.  If approved, property taxes in the district would go up 14.7 cents per $100 of assessed value.  The district says the average district property owner will see a tax increase of about $38.05 per year.  The polls are open from 10 a.m. to 8 p.m.