A Note for Alex (because I couldn't track you down elsewhere):

No - I am not Implying in chapter 9 that Snape was in the same year as the Longbottoms. We know so little of them, but this is how my mind works:

I believe the Longbottoms would have been older than the Potters and following, but not by much (Jo seems to have compressed that entire group of central charactes into a 10 year spread, from the ones we absolutely know in canon).

I place them at Hogwarts slightly after Lucius Malfoy(1964-1971), in and about 1968. This would make their careers at Hogwarts from 1968-1974, or about four years after Malfoy.

Snape, as we know, attended in 1971, his first year and Malfoy's last. I believe that Malfoy saw his proclivities and talents and probably started to work on him immediately (this is of course assuming that he really did know more dark magic than most seventh years...shrugs) by drawing him into a tight circle of the 'awful' children Lily hated so much. I think in part this is why it was so hard for Snape to really hear her when she asked him to stay away from his mates. In all honesty I don't see a poor street-rat getting in with the privileged few unless someone like Malfoy pulled a power play. And Snape and Malfoy seem entirely too close for people who attended so far apart... so that's my rational.

Malfoy was gone in 1972, however I leave the Longbottoms in school until 1974, which gives them two more years with a Snape who's already 'in' with the crowd. This means Snape's had time to hear all about the longbottoms, and to get to know Alice... and to hear the rumblings from his mates when she wouldn't commit to Voldemort during her time at school. He would also be aware of her reputation from the Gryffindor side, as canon establishes a firm, if secretive friendship with Gryffindor Lily. - You'll note that he never speaks of Neville's father from personal knowlege ("from what I understand...")

My timeline, which perhaps looked cloudy upon a second reading (that I'll give you), goes like this:

1971 Malfoy notices a young Snape and grooms him

1972-1974 Longbottoms and Snape are in school together. Snape is very aware of school politics and gossip. He's friends with older students as well - mostly those in the few years ahead of him, but with a few of those in Longbottoms' year, because of Malfoy's machinations. He's not particularly close with Alice, though.

1974 Longbottoms leave and marry (they've been in love the longest, and the UST is probably enormous, considering they were in opposing houses. Plus Jo is nothing if not consistent). They enter into auror training. (or not. You're decision)

1975-6 Commence with careers.

1978 Order of Phoenix arises. Longbottoms join, with others, notably the Potters. LOL. Snape as well as Potters etc. Leave Hogwarts. (Feel free to have them marry here. Once again UST and a sense of apocolypse will do that to a couple. I know from experience, lol)

1979 Peter Pettigrew starts passing information. Longbottom's choice is discovered. Her old schoolmates are infuriated. Bellatrix in particular (you choose why).

1980 Neville and Harry are born. Rosier and Wilkes are killed by Aurors (I'm saying it was the Longbottoms). Hatred of Longbottoms intensifies...

August -October 1981 Snape joins Hogwarts staff. Voldemort falls.

November 1981-January 1982 or thereabouts .Bellatrix, Rodolphus, Rabastan, and Bartemius torture the Longbottoms, are subsequently arrested. Longbottoms are committed.

Hope that clears up any confusion. Please feel free to correct any timeline errors, as I'm not by any stretch of the imagination an expert on canon.