It seems no matter how hard I try to keep my art students clean sometimes they still get Acrylic paint on their clothing. But do not fret and please do not throw out their favorite shirts. Here a few tried and true ways I have found to get those nasty stains out.
if you catch it right away run cold water over paint stain. It should come out rather quickly if the garment is cotton.
If you do not have access to water, baby wipes sometimes can take out the paint, but be careful not to spread the paint all over the garment.
If the paint has dried then Rubbing Alcohol works miracles. It can take a bit of scrubbing with a tooth brush, but it will eventually come out.
Washing clothes in OxiClean has been known to take out tough paint stain.