Mountainside High, the sixth comprehensive high school in the Beaverton School District, opened Tuesday morning, welcoming freshmen to the the gleaming $185 million building and grounds.

Sophomores will join them Wednesday for the debut school year in the building near South Cooper Mountain at the southwest edge of the sprawling school district.

Principal Todd Corsetti called it an "amazing, amazing facility." It includes a commons space, a large interior courtyard, a recording studio, four turf fields, a large wood shop, a theater, rooftop solar panels, a main gym and additional dance space.

Activity director Erik Reinholt led incoming freshman through a series of team-building exercises Tuesday morning in the gym. The activities were designed to create a sense of community for the students, all of whom are the new kid this year.

"Don't be that person who is too cool for school," he advised the class of 2021. "Revoke that cool card, have fun and make the most of it," he said.

Tuesday was the first day of school for students not only in Beaverton but also most other Portland-area districts, including Hillsboro, North Clackamas, Tigard-Tualatin, David Douglas, Reynolds, Forest Grove, Oregon City and Sherwood. (In most of those districts, students in grades seven and eight and high school sophomores through seniors start class tomorrow, after the first-year students at middle and high schools get their footing.)

Despite sprawling more than 300,000 square feet, Beaverton's new high school will operate with just two grades this year, adding new freshmen the next two years as it grows to its full enrollment, projected to be roughly 1,750 by 2020.

Most students whose homes are zoned to attend Mountainside would have attended Southridge or Aloha high schools had the new school not opened.

Beaverton High is the oldest high school in the district. It opened 101 years ago.

-- Beth Nakamura and Betsy Hammond

betsyhammond@oregonian.com