Denis Cooverman didn't want to give a typical graduation speech, cherishing memories and embracing challenges and crap. So, instead, he stood up in front of his 512 class-mates and their 3,000 relatives and said some-thing really important: ''I love you, Beth Cooper.'' It would have been such a sweet, romantic moment. Except that: Beth, the head cheerleader, has only the vaguest idea who Denis is. And Denis, the captain of the debate team, is so far out of her league he is barely even the same species. And then there's Kevin, Beth's remarkably large boyfriend, in town on furlough from the United States Army. Complications ensue. Denis comes of age overnight in this exhilar-ating, endearing novel that reminds us why we can't wait to escape high school but can never leave it behind.