School started Tuesday at new elementary schools in Portland and Falmouth. It was the first day for many at Portland’s Ocean Avenue Elementary School, which replaced the aging Clifford Elementary School. Students who attended Presumpscot, Longfellow and Riverton schools started at Ocean Avenue on Tuesday, bringing enrollment to 430. It also was the first day for more than 870 students at the new Falmouth Elementary School, which replaces the Plummer-Motz and Lunt elementary schools.