McGraw Hill
Mc Graw Hill: Conventions of Standard English: Avoiding Vague Pronoun References
Read about vague pronoun references then click the practice button to practice what you've learned.
Sophia Learning
Sophia: Unclear Pronoun References
A screencast lesson [4 mins, 18 secs] explaining unclear, ambiguous, vague, and indefinite pronouns as well as how to avoid them while writing.
Robin L. Simmons
Grammar Bytes: Pronoun Reference Power Point
Learn about vague pronoun references and practice identifying them in questions that could be found on standardized tests.
University of Richmond
University of Richmond: Confusing Pronouns
This site discusses the need to avoid ambiguous pronoun references. Includes a helpful rewriting examples. Brief, but informative and factual.