I am after the following user interface allowing kids to learn simple arithmetic on their Android smartphones or tablets:
Imagine many flat-cylindrical tokens such as the ones used in the game of trida. You can drag the digits 0-9 stacked vertically on the left onto a checkered square paper space on the right. Two numbers for subtraction or division or two or more numbers for addition or multiplication are automatically generated according to specified number of numbers and number length for each of these. The numbers are placed on the touchscreen automatically and at random and then the user drags each number from the left to the appropriate place. The checkered square area is infinite so as to allow for infinite-length numbers; the area can be panned (and willingly also zoomed). At the end of the homework task the user presses the done button at the top left of the screen. The program goes through the computation searching for the first error encountered and marks that digit red. The user can then erase the following digits and proceed from the red digit. User can make points with solved additions, multiplications, subtractions, and divisions.