Kids don't grow at a constant rate. As you may have recalled from your own childhood, kids alternate between weeks or months of slow growth and the occasional "growth spurt". While this can be difficult to predict, these tend to occur more in the spring.
Other major trends in growth spurts are the major growth spurts from age 8 to 13 for most girls and the growth spurts from age 10 to 15 for most boys. Of course, the biggest growth spurt by far is the one at the first year of your life. You can expect a baby to grow roughly 10 inches before its first birthday.
More information on how kids grow in KidsHealth.