You want to inspire classmates to return for your class reunion and the best way to do is to determine what links your classmates, such as humor, nostalgia, school pride or events tied to the reunion. Since you volunteered to compose the invitation, you probably are more gung-ho about the reunion than at least half your classmates. Consider that and be gently persuasive rather than just writing a formal announcement of the time and place.
Nostalgia and Humor
Remind recipients what things were like your senior year. Mix in humor with the nostalgia. Headline with the year, such as "1985" or just "'85!" then make a list of that year's news and historical events, cultural happenings and your town's or school's happenings. Include top movies and songs, dance, clothing styles, hair styles, quotes from famous people, advertising slogans and possibly prices of things. There are plenty of websites, such as the People History, to supply you with information. Depending on your skill and time, you might include photos. Don't be maudlin. Unless you are writing an invitation for the 40th or 50th reunion, avoid poetry or sentimental quotes.
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A Happy Collage
Go through the yearbook, picking out an assortment of photos of classmates having fun. They don't have to be partying; they can just be a group of kids laughing or doing something silly. Put them into a haphazard collage. Use as your headline, "So, do you still know how to have fun? Prove it!" or "Have the Time of Your Life … Again!" In the subhead, write, "You are most warmly invited to attend the anniversary of Union High School Class of 1992!" Then state the particulars, including the date, time, place, attire and RSVP information. You may need to include theme, food or other necessary event details, such as any admission price or requested donation to the school.