Q: How many kids with ADD does it take to change a lightbulb?

Q: How many kids with ADD does it take to change a lightbulb?
A: Let's go ride bikes!

This is a lightbulb joke and also a joke that makes fun of people with disabilities.

The standard format of the lighbulb joke "How many ... does it take to change a lightbulb? #. 1 to change the lightbulb, and #-1 to do [something that ... are usually associated with]".

This version of the joke circumvents the normal ending of the joke because it just does the [something that ... are usually associated with] part. Riding bikes itself is not associated with kids with ADD, however not being able to focus on the task at hand is.