My family is perhaps rather unusual as we have a family tradition of talking a great deal about children, what children do, how children behave, what children say. I married into a rather similar family. This means dh and I between us have an oral record going back to at least the 1890s in 2 different countries & different social settings, mine involving a large extended family. General conclusions:
c 3/4 of the worried behaviour threads on MN are things I was already prepared for because of what my mother did in 1936 or my gran said in 1902- so small children probably don't change that much
some children in every generation (maybe one or two) have had specific issues and needed to be dealt with in very specific ways; this has nothing to do with general societal trends
with the caveat that you may have to be inventive in the way you deal with specific issues/troubled children, it is generally possible to bring children up to behave in public
child-rearing is work in progress - getting to your goal may take time (hence the plethora of family anecdotes)
smacking has not been used in my family for at least 5 generations and we still manage to turn out children who know how to behave at dinner parties
a bit of challenging on the way doesn't mean either that you are a shit parent or that your child is beyond redemption (my grandmother who lied about her naughtiness c. 1902 and my mother who cheeked her aunt round about 1936 both grew up into highly respectable citizens)
modelling seriously, seriously helps: if you consistently show that you yourself feel a strong need to behave well in public even when you don't feel like it, there is a good chance it will rub off
a certain amount of family loyalty also helps: not thinking your child is always right, but not talking about them as if they were little shits either; showing that you like spending time with them; listening to their pov even when you are going to enforce your own; understanding them doesn't mean caving in