The rider switch pass, or often referred to as the "parent pass", is a little known system that Disneyland uses for their height restricted attractions. In an effort to help guests with younger children enjoy attractions that their child can not, Disneyland has set up a system to enable guests to 'switch' off without requiring them to wait in the line a second time.
The system is nothing new, but it is underused. Let's just say that mom and dad want to ride Space Mountain, but little junior does not meet the height requirement or is too scared to ride because it's dark in that strangely shaped mountain. Mom and dad can go to the entrance of the line for Space Mountain and ask the Cast Member for a "rider switch pass". The Cast Member, having verified that the guests have a child with them, will then issue the parents a rider switch pass ticket. Dad can then wait in line for Space Mountain and enjoy the attraction while mom stays with little junior. Once dad is done with his intergalactic adventure, he can then take his turn watching junior while mom takes the 'rider switch' pass to the Space Mountain exit Cast Member. The Cast Member will take the pass and allow her on the attraction via the much shorter guest assistance line. This allows both parents to enjoy Space Mountain without standing in the main line twice!
The scenario above is a simple one. The rider switch pass can work for up to two guests at a time, so in a larger group someone could potentially ride twice. To take advantage of it even further, the rider switch pass can be used in conjunction with a fast pass. Also, rider switch passes don't have a return time restriction like a fast pass does so you can return later in the day if you choose to do so.
You can obtain a rider switch pass from the Cast Member at the front of any attraction with a height restriction. Just be sure to bring the child with you and ask where to return to, each attraction is different.
Flickr user gruntzooki's photo used under a creative commons licence; no association with OC Attractions