Ben, I'm not convinced that is a Jade as the leaves look very 'thin', hopefully someone will help on that matter. Need a few questions answering though...
Where is it placed in relation to the light source?
Is it kept warm/cold etc?
What type of compost is it in?
Has the pot got a drainage hole?
Sorry for all the questions but they will help determine the problem with your plant and enable us to suggest a possible remedy.

Gill UK

More light, more light, more light.

This plant appears to be Kalanchoe luciae, very deprived of light.

Thanks for your replies. This plant has been sitting in my mud room for the past six months getting an enormous amount of light. Light from three sides...

I have a regular jade plant there, too - it has grown a lot, but is tall and hasn't filled out to support itself. I would have guessed that it needed more light if it weren't for the fact that this is a very, very bright room - and it's been summer!

Gill, to answer your questions:
Temperature: I'd say between 70-80 for the past 3-4 months.
Soil: Cactus Mix Potting Soil.
Drainage Hole: yes, though I just looked through it and there appears to be mold.

Sorry, but it is definitely a light issue. People often underestimate how much light succulents need. They are generally not indoor plants for this reason, but can possibly be grown in a south-facing windowsill or in a windowsill facing another direction augmented with fluorescent lighting. Still, they won't really thrive unless outdoors in a sunny environment. Mine are indoors 7 months of the year with T5 fluorescent lights in a north-facing window, and it's really just about keeping them alive until they can go outside again - they're not at their best.

Also, based on your description your jade is having the same problem. They will grow up or out with long stems trying to reach for light but won't fill in or get color if they aren't getting enough light - they will stay green with leaves farther apart than is typical for the species.

Thank you, spapa. This is exactly what I wanted to know. Sounds like my days of raising succulents are over!