Although only three slides long, this presentation does a good job in introducing negative prefixes to upper elementary writers. Pupils are encouraged to use a dictionary and a thesaurus in order to help them come up with the proper...

In this negative prefixes learning exercise, students fill in the blanks with the correct word with a negative prefix. Students complete 10 questions total.

Tutorial explains how to use negatives to express sentiment.

In addition to addressing the misuse of "irregardless" for "regardless," there's a lengthy discussion about the meaning of negative prefixes, as well as other prefixes that can be confusing. A great reference.