Hundreds Board

The wooden hundred's board is the commercial version of our 100's Grid http://mamadrool.blogspot.ca/2015/10/100s-grid.html
It costs considerably more, but you can expand your game options with the removable pieces.
https://www.amazon.ca/gp/product/B0141B91AI/ref=oh_aui_detailpage_o02_s00?ie=UTF8&psc=1

There are 100 pieces, so this was saved for when I had ten minutes of time with O.
I started by removing five random squares and asking her to find their spaces.
This proved to be very difficult, so we took a new route.

I removed ten horizontal or vertical rows. This was much more straight forward, as she could clearly locate the consecutive number patterns happening in the rows and columns.

She then suggested I take a turn and thought herself especially amusing when she removed horizontal and vertical rows. She was working hard to stump me and as I took my time finding the locations, she walked me through some pattern recognition!