How can I make my (American style) pancakes light and spongy?
I can't say for sure what is wrong, but here's a few possibilities:


Your mix is too runny: if you have a batter that's too thin then it will spread out too far on the pan, if it's too thin you will get a rubbery pancake. It doesn't take much liquid to get too thin, a couple of tablespoons of milk make make the difference between just right and too thick. If you overrun you can always add just a bit of flour
Your mix is too thick: if your batter is too thick then it will be to stodgy to rise well. You'll get a taller pancake but it won't open up
Over-mixing: flour has protein in it called gluten, and developed gluten is what makes bread stretchy. Gluten is developed by working it in the presence of moisture, causing gluten strands to uncoil and interlock. Gluten development is good for bread but bad for pancakes risen by baking soda or powder. If you over-mix your pancake batter you will develop the gluten in it, so it's best to do it by hand for as short a time as possible. Don't worry about eliminating all lumps
pan too hot: if you have the wrong pan temperature it's easy to overcook your pancakes. If it's too hot it will overcook the outside before the inside is done
pan too cool: If it is too cool then you won't get as much lift, or you lose lift because the batter doesn't set quickly enough to hold in the air, and then you have a close texture. You will also need to cook it longer to get it done, getting a rubber mat instead of a light and fluffy pancake
Not enough baking powder: Your recipe calls for 4 tsp of baking powder for 3 cups of flour. The non-buttermilk recipe I use would call for 5 tsp. Probably not enough to make the difference between rubbery and fluffy but you never know.  


Like others in the comments I also recommend buttermilk for your pancakes as it gives better color, flavor and texture. You can make good pancakes without it for sure, but if I have it available I will always use it.