To me it's lots of things, first and foremost CURRICULUM. How much is being taught?
We moved to a lovely, safe, small town in scenic region into a lovely house affordable enough to manage on one income while I raised the kids and didn't pay attention to school district, thinking we'd move by kindergarten or so for my first. But here we are, divorcing, unable to move at this time, and I'm homeschooling. Why? CURRICULUM.
The district is lowly rated with good reason. And that's in the US which is lowly rated on a global scale, so a bad school in the US is a BAD school in the world. Not only for test scores (which don't matter, because some schools have great test scores because their curriculums are so easy and lacking). I researched long and hard to find out what a good kindergarten should cover for a thorough classical education at competitively global standards. We have lots of foreign friends (German, Australian, Canadian, Japanese) where we know musical instruments and a foreign language are standard in kindergarten. We KNEW that was unheard of here, so we were willing to do outside tutors for those things. But even the BASICS were lacking when I interviewed the teacher to see what topics would be covered.
My daughter is in the end of her first grade year now, reading at a very advanced level, mastering an advanced math curriculum, learning lots of geography and history, doing science experiments, does lots of memorizing of classic poems, and grammar and writing, writes beautifully in cursive and manuscript. We do tons of hand on activities out and about with homeschool network as well. She also has French lessons violin, piano and Ta Kwon Do. In other words, we have ASSEMBLED the standard type of education she would get at an excellent or international school. She's ready to go into second grade and would be LEAGUES ahead of her peers. Her friend in our public school can barely read, her writing is terrible, they dont teach cursive in PA anymore, they're doing NO history or science and haven't started formal grammar, and they're doing the random "memorization math" that has American kids entering colleges at worse and worse math levels every year. This girl is every bit as bright as my daughter but is getting almost NONE of the academics we are offering in curriculums that are readily available to people.
The best teachers in the world don't matter when the subject matter they're forced to teach is whittled down to only what is on the standardized tests.
Once you have a thorough curriculum being covered, you of course need great, enthusiastic teachers who can inspire, a safe facility with lots of supplies and resources, nice student and parent population and all the other "school stuff". Some districts are in dangerous neighborhoods.
None of that pertained to us though. For me it was making sure my child is academically on point each of her early years to set a good foundation, and in our school, it's the lowest common denominator. It's not a super brainy town either. It's nice and pretty, but not brainy.
I do have some friends in wealthier districts who have schools that are comprehensive in material as well as being nice facilities with great teachers. It's why the wealthy in this country will continue to be the most educated and the classes will keep dividing into the future. The socialist education agenda set forth by Abe Lincoln and co. to educate all children equally is long gone.
I don't know what you mean that your children are expected to learn more than you did. The curriculums have plummeted sharply since the 50's and even more since the 70's. Kids are learning WAY less now. Pick up a Core Knowledge Book from any grade from before 20 years ago and you'll see the years are far more advanced than what schools today teach. My parents worked full time in 70's and I learned everything at school. Today that is not the case for kids and the school I went to then is now rated the worst in it's district.
With your support, you kids will do great in school. You just want to be be sure the school is teaching enough imo. Straight A's and loving school aren't super important if the education is lacking. If it's a rural area, be sure it's not the kind of rural area that doesn't value education. The treatment from schools in our area for the past seven years with defunding, schools closing, and program cuts to science, social studies, the arts etc... has been deplorable. Corbett has made it even worse.