The Star Trek Club and the Middle Earth Club of Mira Loma High School merged in 1979 to form the Science Fiction Club, and the Order of Excalibur Club was added in 1980 “to congress around Dungeon and Dragons and other board games revolving around wizards and magic.”
The graphic on the D&D shirt appears to be the same one the kid in this D&D Club is wearing. The letters are iron-on affairs, so my guess is there was a generic dragon shirt on the market at the time, and the kids had mom press on the letters. Another homegrown D&D shirt here. Lots more D&D Clubs here.
(Image and background via Mira Loma Alumni and Friends)