The clock is indeed a Gilbert schoolhouse clock, sometimes called an office clock. They were most commonly made as time only clocks (no chimes) so they would not distract workers or students with an hourly chime.
The clock in your picture was called the "Admiral" and was time only. It was manufactured in Winstead, CT. (before they changed the name of the town to Winchester) circa 1900.
In my most recent book, which is from 1999, the value was listed as $1,350. This was for one in good condition, all original and running properly.
Looking at your picture, the dial, case, hands and pendulum do look original.
That is a very nice clock - thanks for posting it.