I then came across this photograph of what was called District Number 3 School, built in 1899. The architecture of the school is very much similar, and is otherwise an exact match of Pleasant Retreat Ridge with the exception of the bell, which could have been later removed.
A fairly crude map from 1921-1922 of the schoolhouses in the county excludes Pleasant Retreat Ridge.
The antiquated schoolhouses were consolidated into the new Trimble County High School in 1932. I assume that a companion elementary school had been completed at around that time.