New Zeros:

Players are allowed to use a turn to place a new starting 0 anywhere on the board at any time.

Add 'Em Up:

Once the board is full, add all the numbers of each color. The player with the higher sum wins.

Skip-Count:

Instead of adding 1 when you write a new number, add 2, 5, 10, or whatever number your child is learning to skip-count by.

Writing Numbers:

At its simplest, High Ground is a good chance for the very young to practice counting and writing numbers.

Drawing the Grid:

Drawing the grid can itself be a good learning opportunity, and a chance to practice spatial reasoning. One way to do it is to first draw two lines across the middle. Then, draw a line across the middle of the top and bottom sections to split them each in half.

When drawing the first two lines, you want the space on the top and bottom to be twice as large as the space in the middle. That way, when you split the top and bottom sections, you have 5 equal rows.

While you're at it, you can ask questions like "How many lines do you think we'll need to draw to split this square into 5 rows?" or "How many little squares will there be when we've drawn all the lines?"

Strategic Thinking:

One way to investigate the strategy of a game is to play with a specific focus in mind. Before you play, decide if you will focus on offense (reaching as high a number as possible) or defense (trying to block your opponent). Let your opponent choose what their focus will be, too, but don't tell each other before you play. Afterward, see if you can guess what your opponent was focusing on. Ultimately, of course, both offense and defense are important.