Why did they replace all the blackboards at Thanksgiving in war time, I wonder?
That’s a really good question. There was food rationing during WW I and it began before the boards were changed out. I’m guessing we weren’t in the war long enough to require other rationing as we did in WW II.
From http://histclo.com/essay/war/ww1/cou/us/food/w1cus-usfa.html:
A few weeks after America entered World War I, a volunteer organization was established (May 4, 1917). It soon became apparent that the War required a much greater Federal effort to address the issues concerned with food production. Food shortages began to appear as prices were rising in 1917. President Wilson established the United States Food Administration (USFA) as an independent agency by President Wilson with Executive Order EO 2679-A (August 10, 1917). The President acted under the authority of the Food and Fuel Control Act (40 Stat. 276), August 10, 1917. The task assigned to the USFA was to regulate the supply, distribution, and conservation of foods. The USFA bought and sold grain and sugar and their products through two subsidiaries: the Food Administration Grain Corporation (U.S. Grain Corporation) and the U.S. Sugar Equalization Board, Inc.