Holding down the option key isn't allowing me to select Windows/OS X on startup

I have Windows 7 installed on a 15-inch Retina MacBook Pro.

According to Apple's Boot Camp Installation and Setup Guide, pg. 10...

Select an operating system during startup

You can select which operating system to use during startup by holding down the Option key.

This displays icons for all available startup disks and lets you override the default setting for the startup disk that is in Startup Disk preferences (OS X) or the Boot Camp control panel (Windows), without changing that setting.

1 Restart your Mac and hold down the Option key until disk icons appear onscreen.

2 Select the startup disk with the operating system you want to use, then click the arrow beneath the icon.

I'm finding that holding down the option key has no effect -- the machine boots into whichever OS was last running.

This is true whether I'm starting from the shut-down condition, or restarting.

I've tried hold down each of the two option keys and I've tried holding down both at once.

I've tried pressing the keys from before the startup chime and just after.

The only way I've been able to control which OS starts up is to restart from the Boot Camp control panel in OS X in either OS.

Any thoughts on how to get the machine to behave as described in the docs?

I had a similar issue and the below trick solved it.

Resetting NVRAM

1. Shut down your Mac.
2. Locate the following keys on the keyboard: Command (⌘), Option, P, and R.
3. Turn on your Mac.
4. Press and hold the Command-Option-P-R keys immediately after you hear the startup sound.
5. Hold these keys until the computer restarts and you hear the startup sound for a second time.
6. Release the keys.

^{Source: https://support.apple.com/kb/ht204063}

There are 2 methods if the Option key doesn't work.

METHOD 1 @Amol mentioned it, his answer is perfectly correct. On your Mac, go to:

System Preferences > Startup Disk

Now click the Operating System that you want your next start to boot into.

Truly simple.

METHOD 2

Download rEFIt and install it. Then reboot.

You might need to reboot twice or more before the rEFIt menu starts showing up on boot.

Good luck :)

Two things to try:

1. Hold Option before pressing the power button and don't release it until you see the Boot Menu.

2. If that doesn't work, try resetting your Macbook Pro SMC as explained here.

Just go to System Preferences in Mac and choose Startup Disk. It will give you choice of Windows or Mac as want for your next start up of your computer.

Through experimentation, I found that disconnecting the Apple extended keyboard from an unpowered USB bus and reconnecting it directly to a USB port on the back of my Apple Cinema Display fixed this problem. Apparently the firmware that's necessary to choose which partition to boot from won't act on holding down the Option key otherwise.