Do most flight schools and FBOs in the US prohibit student pilots from practicing stalls while flying solo? Do most flight schools and FBOs in the US prohibit student pilots from practicing stalls while flying solo?

This question is asked in the context of civilian flight training in single-engine land airplanes.

I've heard of this policy actually being in effect with at least one flight school.

"Most" means more than half. "Student pilot" is not meant to include anyone who holds a pilot's license for airplanes or for that matter for gliders.  

The reference to FBOs means that they are renting an aircraft to the student pilot involved.

The question is asking about a blanket prohibition that would include a student who is close to being ready to take his or her checkride, not something only applied to (for example) the first few solo flights.

People who have had personal experience with a large number of flight schools and FBOs will be in the best position to answer this question.
The two flight schools I have used had this rule and all of the other local places I know of also have this rule. The FAA no longer recommends full break stalls during training anyway you merely need to bring it to the horn. Interestingly enough the data does not support the decision 


  Student pilots are, by far, the least likely to suffer stall/spin
  accidents, as a proportion of in the pilot population. Pilots holding
  FAA Airline Transport Pilot (ATP) certificates are also less likely to
  stall/spin.


Although a case can likely be made that limits like this are what make student pilots least likely to stall/spin.