20 April has more than one anniversary attached to it.
For the purpose of this thread topic,
the student activists of this year
observe 20 April as the date of the Columbine High School mass killing.
It was in 1999, nineteen years ago.

On that day a National School Walkout is planned.

Journalists (CNN, eg) have pointed out that
no small number of today's high-school or junior-high-school activists
were not yet born on 20 April 1999.