I have a feeling only approved political activism would be accommodated so reasonably by school officials like this was. I'm not sure a pro-life walk-out would be met with such understanding and willingness to allow students to protest.
And on that note, where do we draw the line? If we can have students walk out for gun control, can we have them walk out for various causes throughout the year? Maybe a walk-out against the war in Afghanistan, or to protest Guantanamo Bay? This is a cool concept, using schoolkids to bolster a political cause, maybe there's room for expansion?