There's a wooden beam in the basement of my parent's house that is covered in marker. Besides holding up the floor above it, its main purpose was to track the heights that my sister and I achieved each year. I was about six years old, my sister two, when we moved in, so the beam has plenty of marks. There's also visible proof that my younger sister bested me in the height department. I'm sure that there are plenty of houses with hash marks (accompanied by names and dates) - door frames, closet walls, even basement beams- recording the vertical advancement of the children within. There are even removable wall-hangings that you can purchase to track your kid's height, should you chose to go that route.
When our son was born, I wanted to document his growth, but there aren't any wooden beams in our basement and a cardboard wall-hanging didn't seem permanent enough for me. I wanted something lasting but practical.
I was measuring a window for curtains when the idea came to me: a tape measure.
Small, compact, and sturdy, a tape measure was the perfect way to track my son's growth. If we move, it moves with us. If we want to paint, we don't have to worry about accidentally covering anything up. And, it'll grow with my son...as long as he doesn't exceed 12 feet.
So, I went out and bought a retractable measuring tape from the local hardware store for about $4. I wrote his name and date of birth on the side, and with a permanent marker in hand, I've been tracking my son's progress on the metal tape. Today, I added his official 18-month height from the pediatrician's office.
For those soon-to-be, new, or already parents looking for a new way to track your little one's growth, I highly recommend the tape measure method. It's affordable, easy, and mobile. Major perks when it comes to keepsakes.
Just a quick word of advise: pick a plastic-case tape measure so you can write names/birthdays on it and make sure it's at least 6' long to accommodate potential height.