Congratulations. That baby boy or girl you used to put in diapers and onesies is ready to put on a cap and gown and walk across the stage to pick up that high school diploma. You're understandably proud and want to ensure your attire is appropriate as you celebrate your child's achievement at the graduation ceremony.
Indoor / Outdoor
First, consider whether the ceremony will be indoors or outdoors. You'll want to wear semi-formal, business or business casual attire in either case, but you'll also want to dress appropriately for the environment. If the graduation is outdoors, choose an outfit appropriate to your area's climate. You'll want to look nice, but you'll also want to be comfortable. If the graduation is indoors, consider whether the area is air conditioned. You'll want to wear lighter clothing if the ceremony is in the school's gymnasium or another environment without air conditioning.
Check with your son or daughter's school to see whether they have a dress code for the guests at the graduation ceremony. Most high schools are fairly flexible -- they want all parents to see their students graduate, but some are not. If the school has a dress code, adhere to it. In rare cases, schools have refused admittance to parents whose attire did not meet the school standards.
Barring a specific school dress code for graduation guests, fathers should aim for business or business casual attire. A suit is always an appropriate choice for graduation ceremonies. For most high schools, a pair of dress slacks and a button down, with or without a tie, or polo shirt are acceptable attire for male graduation guests. Don't wear jeans, T-shirts, shorts or other casual attire and avoid any sort of clothing that would draw undue attention -- the attention should be on the graduates.
Mothers should wear semi-formal or business attire. Dresses are a good choice, as are a coordinated skirt outfit or a pantsuit. All clothing needs to be in good taste and not too flashy or attention-grabbing. Wear clothing in colors that coordinate well with the school's graduation gown colors. You don't want to clash in the pictures you'll take with your student after the ceremony. Keep makeup, accessories and jewelry understated and tasteful.