The window note card die cut (AccuCut WN200J) may be used as a self-checking device. Write a math problem in the window panes. If laminated, students could write answers on the laminate with a dry erase marker. Then the student can open the card to check the answer.
You may do something similar for spelling words. Paste a picture behind the window. Open the card to check the spelling.
You can make a slide quiz device by stapling two note cards back to back. Cut a card that will fit inside. Remove the window frame. Paste a question on the card to fit in the window. Pull the card out to reveal the answer. Flip the frame over and attach another question and answer to the back opening.
Students can cut out pictures and paste them behind the windows to create books. Alternating the windows from left to right and then stapling down the middle will allow the window to be every other page in the booklet.
Create an interactive bulletin board. Cut the card a little narrower to create the proportions of a door. Write questions on the outside and answers underneath the doors. A brass brad will give the appearance of a doorknob.
Make a little house by adding a roof and door. You may want to make the door so it can be opened to reveal a picture.
Don't forget to save all the little window pane cutouts. Use them for arrays, counters, game board paths, and mosaics.