If something is bitty, it is made of small parts that do not seem to belong together. A bitty report hops from point to point. A bitty conversation never settles. Teachers and reviewers in Britain use this a lot; it is informal-to-neutral, a little critical but not unkind. Though actually, you will also hear bitty in another, softer way, especially in American English: itty-bitty (and sometimes just bitty) meaning very small and cute. That is a different use. And drink or soup can be bitty in a more physical way — little bits floating in it. The sense you need for most school writing is the first one: not joined up. It comes from bit, a small piece, plus -y, ‘full of / like’.