What are some funny (yet short) skit ideas?

Tomorrow, since it's the last full day of school (we get out on the 14th, but the rest of the school days are half days), my math teacher has decided to do a talent show! And, wouldn't you know it, my /smart/ friend just so happened to sign us up to do a comedy skit. And I, the lucky duck, have to come up with an idea and write the script because my friend is idea-less. And, just to make everything MY problem, she is by her dad's house tonight and can't use her phone to text me to help me with this. So, please help me think of an idea for a comedic skit that'll amuse 11 year olds in 5th grade.