Education
In reply to the discussion: do you think teachers need a dress code? [View all]FBaggins
(28,706 posts)"Professional" has never meant "you are your own boss". In general it refers to a person holding a position that requires specialized knowledge/education (as distinguished from training).
With some exceptions, if you can hire a reasonably intelligent person of the street and train her to do the job, it probably isn't a professional position. If you (usually) need an advanced degree in a specific field in order hold the position, it probably is.
The pharmacist is a professional whether he owns her own pharmacy or works for a chain. The attorney is a professional whether she has her own firm or works for law firm or works as an in-house attorney for a firm in another industry.
The one who works for a company is no less a professional because of the company's dress code. The sole proprietor doesn't have one because she doesn't need one. If she isn't dressing much the same way, she won't be in business for long (as she demonstrates daily the difference between the noun and the adjective - she is a professional who is not professional).
On edit - regardless of whether you accept that definition or not, your post requires us to revisit the OP. What you're saying is that you don't consider teachers to be professionals... right?