Construction on a new Lower Merion High School will officially begin today, with a groundbreaking ceremony at Arnold Field, on the Montgomery County school's campus in Ardmore.

The ceremony, at 10:00 a.m., is open to the public.

Over the next 28 months, the new 1,250-student high school will be built behind the existing one. When the new school is occupied, in the fall of 2010, the old one will be demolished, except for one building. The cost of the new school is projected to be $108.5 million.

Work on a new Harriton High School in Rosemont, on the same site as the existing Harriton building, began last June, with occupancy scheduled for September 2009. The new Harriton High, which will also house 1,250 students, is expected to cost $103 million.

Contact staff writer Dan Hardy at 610-701-7638 or dhardy@phillynews.com.