Dear Aunt Debbie,
Your mention of bats being banded by humans in the Silverwing series made me think about two very different books involving animal-based lab experiments.
Mrs. Frisby and the Rats of NIMH, by Robert C. O'Brien, is an action-packed adventure story. Mrs. Frisby is a widowed mouse bringing up four mouse children, and when one of her kids is sick and she can't move him to their summer house, away from the garden plowing which endangers them, she ends up seeking help from a group of former lab rats who live under a nearby rosebush. It turns out that these rats were bred and trained at NIMH (the National Institute of Mental Health), and have near-human intelligence and capabilities. They've created their own functioning society, complete with siphoned electricity, but are planning to relocate to a utopian farming community (as in Watership Down, there's a certain amount of exploration of what constitutes a perfect society). The rats help her save her son, she helps them avoid capture, and there's a scene about drugging a very scary cat. I haven't read the book in years, and think it may be aimed at a slightly younger audience than your Watership Down-loving sixth-grader, but I remember being captivated by it.
Flowers for Algernon, by Daniel Keyes, is written from a human perspective, but features a lab mouse quite prominently. Algernon is the mouse, the recipient of brain surgery which makes him increasingly intelligent, to the point where he becomes a kind of mouse genius, solving all possible mazes. The story is told through the journal entries of Charlie, a mentally handicapped man in his 30s who is asked, and agrees, to undergo the same brain surgery. His writing is at first full of misspellings, and reveals his dim awareness of much of the world around him. After the operation, however, Charlie's intelligence increases by leaps and bounds. He begins to understand his own history, forms complex relationships with the people around him, falls in love, and eventually gets so smart that he becomes a bit of a social outcast in the other direction: whereas once people made fun of him for his stupidity, now he makes them feel stupid. In the second half of the book, Algernon begins to lose cognitive function, and then so does Charlie. It's painful stuff: Charlie is at first terribly aware of his waning capabilities, then ultimately loses the capacity to remember and understand who he was under the effects of the operation. Total tearjerker.
Both books cry to be read as metaphors for human interaction and society; both ask you to think about the results, positive and negative, of trying to change the basic parameters of our capabilities. They stick with you, these speculative fictions.