You don't know about getting into other schools unless you try. The most over-subbed school in our county took kids from 30 miles away, few years ago (no SN or special conditions to help them get in).
Need to puzzle thru if the OfSted criticisms are things that can be fixed soon or could affect your own kid.
Problem with asking about discipline policies or setting strategy or what yr they start GCSEs is that it could all change in 3-4 years so be totally different for your kid. Plus, 2bh, there isn't time during Open Evening for all of the questions Soursprout listed. And you'll get different answers from each teacher coz they tend to only understand their own subject/dept.
I like to see ...
Clean & well-organised classrooms with lots of student work on display and energetic staff/kids engaging with the visitors.
Lots of kid helpers keen to help out & working well together.
HTs who don't waffle on but instead let the kids take leading roles in main presentation.
A parent portal or online system so we can A) pay for canteen B) see merits/demerits/recent reports about our kid C) up to date parent calendar of events that is easy to find & use.
Leadership & volunteering opportunities for the kids, junior chambre of commerce, sport fixtures, music lessons, etc.
Lots of celebrating achievements of individual kids in different types of areas
Focus on all-round development, not just academics
HTs who admit no school is perfect but they have multiple strategies to sort out problems (bullying, etc.)
Enthusiasm among the teachers for their subject. At Open Evening I got a 5 minute spiel about the mechanics & benefits of food tech GCSE. Odds are high DS won't attend that school, but it was great to see the teacher liked her job.
Unfortunately, it can come down to gossip, though. I heard a pretty damning tale of incompetence about local school this year, am hoping to steer DS away from there.