老闆 (老板)【lao2 ban3】 can be used when a customer addressing shopkeepers. On the other hand, 老闆娘 is used when a customer addressing a female shopkeeps.
While Cantonese Culture is different. 老闆 (娘) is used when a customer addressing shopkeepers OR a shopkeeper addressing a customer (a wealthy or normal customer). Not just that, people often use 事頭【si6 tau4】 or 事頭婆 【si6 tau4 po4】 (for female) when calling a shopkeeper or a customer. 老世（細）【lou5 sai3】 can also be used to address 老闆 too.
Remember 老闆 or 老闆娘 can be used when business trading, a girl addressing her boyfriend or addressing the boss you are working with.
However, in some cases, 老闆 can be used as vulgar or in prostitution.
- Vulgar: 你老闆！(Similar to 你媽的 or you mother f*cker.)
- Prostitution: It is similar to business trading, paying for some goods or services, like 老闆，你今晚要不要特別服務 or Boss, do you want to have some s*x tonight?
It seems 老闆 these words can be used in everywhere, but be careful when you are using these, because different situation it would bring different meaning.
As you said in a school setting, for example, if the director is the owner can you call them laoban? We usually call him 校長，校監(different from 保安)
What if it's the receptionist and you don't know who the boss/owner is? We usually call him 經理，老總（rude）
What if you work at that place? We usually call him 經理，老總 (polite)，老闆
Note that 老總 is considered BAD when a customer request to see workers' boss. May be the services they provided are bad.
老總 is considered POLITE when a worker calling his/her boss/team leader.