I wouldn't agree that this kid is doing nothing wrong - but clearly he's bright, and clearly he discerns that what he does gets a rise out of his teacher. Speaking from the inside, ladybug, I can assure you that gifted kids like him don't need teachers who are smarter than they are: they need teachers who are wiser. The boy probably does need more challenge in your classroom - but it takes two to make a contest of wills, and if you can find it in your heart to stop thinking he needs to be shut down altogether, you might be able to find ways to turn him from a competitor into a co-conspirator. (The word "concubine" is a bit tricky to discuss in a fifth-grade classroom, depending on how uptight your community is about sex, but not impossible; the word "niggardly" could open the door to an interesting teaching moment having to do with words we don't use because they sound like other words that we don't use because they are hurtful.) As for the inappropriate public displays of affection, try pointing out to him, in a word-to-the-wise tone, that eighth-graders are subject to rules that fifth-graders are not: his indiscretion could land his girlfriend in trouble. Being able to recite chapter and verse from the middle school student handbook will help.