Games like Scrabble and Boggle are great for practicing spelling and vocabulary. Teens with low literacy will practice basic skills, but it is also enjoyable and good practice for those who already have an excellent vocabulary.
Having these games in your library promotes literacy in a fun way. I would recommend having them in a teen area near comfy seating. If you have multiple copies having a tournament could make people aware that it is available and bring more young adults in to the library.