Antique School House Letterboard / Spelling Board

Rare 1900's Antique School House Letter board/ Spelling Board.
Preowned with discoloration, a bit of crackling, some letters chipped, regular wear from use, and there is a sticker on the back (see photos). 
Over 100 years old and works fine!
Made of wood.
Patented in 1889, these boards were reproduced until about 1920's. Children used them to practice spelling words in school.
Pencil writing on back has the name Mildred (a couple hard to read words) and 1903.