how likely is intra and inter district transfer of school in socal?

I know CA permit parent to apply for their children to attend school outside of their original district or different school within their district other than the school they are originally assigned to by default. But how likely is it granted? My understanding is they have to apply each yrs and it's not guaranteed either. There has to be open spaces and also district has to allow it. 

If there is area I like to live but I schools are pretty bad and I prefer my kids to attend different school (other school within same district or school in different district), I want to know how difficult it is. Does it get granted pretty much every time unless the kid or parent has some negative issue? Or it rarely gets granted unless parent or kid has some special condition? or is it 50/50? Have you tried this? or do you know anyone who tried this? thanks.