1. Parent to parent -- the best source of information on a school district is to visit the schools yourself, schedule a tour with the principal or guidance office which will let you see the classrooms, student-teacher interaction, etc. and ask questions of the professional directly. Too many people come to judgemental conclusions based solely on internet data, although looking at school report cards can be a helpful place to start. For instance, I know from a friend of mine who is a teacher in the high school of one "top-performing" district in a nice town who encourages their special needs kids to take ACTs instead of SATs, so their scores won't be averaged in with the "regular" population of students. Just remember that you have to judge what is best for your children. You can also ask your realtor if they know of parents in the town you can call for more information.
2. You answered that question yourself -- you just don't know what will be the various factors that could change a high school's ranking or student performance or makeup of the community over 10 years, although if a school system has a long-standing reputation, that does count for something. In these days of ever-shrinking state aid and tax dollars being squeezed in annual budgets, educators are always looking for different approaches to improving student performance and keeping up standards.
3. If the agent hasn't filled in the correct schools on the NJMLS listing (and quite a few don't), it's either because they don't know which ones or haven't called the district to get the information or don't want to be responsible for giving out wrong information. Many school districts have changed attendance lines as they either restructure their grades or close down smaller schools. There are a few others (like Teaneck) who balance schools for integration so that each school has approximately the same breakdown of ehtnic or racial grouping. The real estate websites like Trulia only look at what is in physical proximity, not what is accurate. The best thing to do is Google the town's school district, and call to give them address of a house you may be considering to ask which schools that location would send your children to.
If you are still looking for a realtor to work with, give me a call! If you have a good realtor, best of luck in your search for a home -- Bergen County is a great place to live!
Coldwell Banker Residential RE/Oradell