Section 6.14 Authors with the Same Surname discusses how to format references and in-text citations for authors with the same last name.
The rule states to include the first author's initials in all in-text citations to help avoid confusion. See page 176 for examples of both references and in-text citations.
All information and page number references are based on the 6th edition of the Publication Manual of the American Psychological Association (2009/10).
Need a copy of the Publication Manual? Click here for details. See Also: APA Style Guide to Electronic References, Sixth Edition