Here's the general outline of how this could work:
1. Let's say your school's music program is having a fundraiser event like an auction or a costume contest.
2. Pick a hashtag for the event and let people know about it. Print it out and plaster it on posters with prompts like, "remember to tag your pictures, #myschoolrocks."
3. Use a tool like Tagboard to monitor the hashtag and reTweet, Pin, reGram, tag, and otherwise help the event's hashtag grow.
4. After the event is over go through and choose a bunch of pictures and or Tweets to create a collage of highlights of the events. Tools like Pic-Collage and PicMonkey make it easy to build collages. (Remember to ask for permission to re-use another person's pictures). Post the collages on your school's Twitter, Facebook, and Instagram accounts. Of course, you'll also want to use the collages in your school newsletter too.
Why do this?
1. Your students and their parents are already likely to be using social media during after-school events.
2. By encouraging the use of and tracking a hashtag you can have a better sense of what is being said about the event.
3. People love to see pictures of themselves (the selfie stick is the new symbol of narcissism) so by including their pictures in news about the event they're more likely to share news about the event.
4. If the event went well, people had fun, and money was raised (or whatever the event's goal was), you now have a small army of people who have positive feelings about the school that they are sharing throughout their communities. Sharing good feelings and comments about your school is always a good thing.