I am sorry to tell you, but kcinmn's recommendation is misleading... and since any private tour will be expensive, it is well to know what exactly is included or is NOT. One thing people do not realize is that Greece is VERY strict about what kind of guides are allowed to go onsite with tourists and explain the ruins, church, museum or whatever. Only LICENSED guides can do this. These experts have to study for YEARS and pass extensive tests & demonstrate expertise & background, to be licensed. Others who do not make this investment in knowledge may pass themselves off as "guides" ... but all they can do is give you briefings while you are driving around, & then hand you a flyer or brochure as you enter the site. And believe me, you can't really appreciate a major site in that way, unless you've done some major homework on your own.
I went to the website link given by kcinmn, and it does NOT indicate licensed guide included... in fact she said "Great info while we were driving." That's well and good... but $60 per person is a lot, even when u consider transport. Not to say you shouldn't do it, just be aware. Fortunately, you've asked your query on the R. Steves Website... and Rick has provided a VALUABLE and FREE way to get the most out of the Acropolis/Parthenon AND Ancient Agora visit... a FREE download of a step-by-step audio guide to exploration of both places. (click on "Watch, Read, Listen" on the LH side of this page & see how to put these on your smartphones or tablets). He doesn't have one for Acropolis Museum, but it has good signage, and helpful docents scattered around. TIP: for the Museum, go to TOP floor first -- because it has a SUPERB 20-minute video that puts the whole history into perspective... also, either before or after you explore the museum, its terrace is a fine place for lunch -- you look right up at the Parthenon, it's open-air or glassed-in with A/C (depending on how hot the day is) ... moderate prices, AND time-efficient, since you have only 1 day.
PS: Whatever tour company you choose, I concur with others to go for the Athens-only option.