High school graduations are important days for the graduate and his/her family. Graduation day represents years of effort and is often a symbolic transition into adulthood. Because of this, high school graduations are typically formal affairs.
Because of their formal nature, suits or business casual outfits including a sport coat are usually required. However, high school graduations typically occur in early summer when temperatures are high. Outside in the sun or in stuffy un-air-conditioned gymnasiums can lead to unpleasant surroundings, so light-weight and light-colored clothing is appropriate.
A nice dress shirt with light-colored dress pants and sport coat is appropriate for a high school graduation. Darker colored pants and sport coats can also be worn, but may end up being too hot depending on the setting.
Ceremonies are often outdoors, so dress in lighter colors and fabrics
Ceremonies can take many hours, so wear something comfortable
The dress code might vary by location in the country. Check our advice about business casual for different regions of the count