please help me!!!!

Put the sizes on the uniforms while sorting them out. and the italicized is sorting them out,can only be:
adverb clause
infinitive phrase
past participial phrase
elliptical clause
adjective clause

I believe it's an elliptical clause.

http://www.englishtutes.com/Parts_of_speech/Elliptical_clauses.shtml

thank you and what about this one:Headed by a senior, the group drew up rules for School Spirit Week.

i think its nominative absolute??

or prepositional phrase with a gerund

Which words are italicized?

senior

The single word, senior is the object of the preposition "by."

so it would be nominative absolute??

No.

Are you sure there are no other italicized words?

i think it could be: Headed by a senior,

its past participial phrase