Hundreds board device comprising a first member having thereon a series of consecutive natural numbers arranged in a ten by ten number array consecutively numbered from one through one hundred; a second member superimposed on the first member and including an array of windows registering with the numbers such that each of the windows has one of the numbers displayed therethrough; a first array of first colored transparent window slider covers horizontally slideably engaged relative to the first and second members for individually opening and closing each of the windows and a second array of second colored transparent window slider covers vertically slideably engaged relative to the first and second members for individually opening and closing each of the windows such that only one of the two colored transparent window slider covers is used at any one time to close any one window for teaching basic mathematical calculations and concepts.