The date of the event is 6 (?) March 1956 (?).
The chief dignitary attending the opening looks like Basil Brooke (Lord Brookeborough), who was Prime Minister of Northern Ireland at the time.
There's a lot to look out for in the video. Here are a few highlights that I spotted:
0:46 - two girls passing the time by side-stepping in unison
2:20 - the cameraman films his own shadow
3:00 - a panoramic shot of the school body
3:19 and 4:30 - a flurry of press activity
5:12 - two boys in a hurry
6:52 - a flamboyant show of deference
7:00 - cigarette butts
7:34 - a peek at the new labs
7:56 - the choir