A day late... but the truths are still relevant.
If you want to do one thing that can make a tremendous difference. Something with an impact that resonates. Something that's been proven to make a difference, in the hardest places and for the poorest people... educate a girl.
October 11th was International Day of the Girl Child.
Here is Malala Yousafzai's Nobel Prize acceptance speech
Also, worth your time, and great for teens:
Half the Sky