It's a touchy subject, ESY. Still, parents and teachers and administrators are supposed to sit down once a year and discuss it. Really discuss it. Not dismiss it off-hand and sweep the subject under the carpet. Istart 7 makes that more likely, but we still have a long way to go.
When does a kid need extended school year? When they will not retain over long breaks the information or skills they got in the school year. When they get "stuck" at break time with a burgeoning skill that should be cultivated. When students have "special considerations" like a degenerative condition or seizure disorder. Unfortunately, I encounter lots of educators who think of ESY as some kind of hand out and not the useful, invaluable service that it is. Don't ask me why. I don't get it.
Parents can advocate for their children with data. Make sure you collect as much data on your child as possible. A trend of regression can usually be spotted in the patterns found in constant record keeping. It's imperative that you collect your own and insist on collection at school. Another important note to remember is that there should ALWAYS be a discussion, a serious, lengthy discussion, on every individual child's needs. This is covered in the guidelines for ESY provided by the state of Indiana.
Case conference committees are supposed to be a collaborative effort. That requires more work than typically observed. Teachers get in a hurry because they are genuinely swamped with work. Parents don't always know what should be discussed and how much is left out on any particular subject. The guidelines (based on case law by the way) are extremely important. When we follow the law and the data, it removes the emotion of the decision. By analyzing our evidence, schools and parents can leave their own baggage at the door and truly focus only on the child, not the cost or fear of failure or anything else.