I had the honor of being a guest speaker for the PHP class at Clark College in Vancouver, Washington. The following is the slideshow presentation and references and resources mentioned during the presentation.
WordPress Codex PHP and Programming References
- Automated Testing
- Conditional Tags
- Data Validation
- Debugging in WordPress
- Developer Documentation
- Function Reference
- Include Tags
- Plugin API
- Plugin Resources
- Query Overview
- Stepping Into Template Tags
- Stepping Into Templates
- Template Tags
- Anatomy of a Template Tag
- How to Pass Tag Parameters
- Templates
- The Loop
- The Loop in Action
- Using Subversion
- Writing a Plugin
Other WordPress and PHP References and Resources
- Using PHP Inside Content of WordPress Blogs
- WordPress functions.php Template with 15 Essential Custom Functions | Digging into WordPress
- Simple Debugging with WordPress | Fuel Your Coding
- Mastering Conditional Statements and Tags for Tweaking WordPress Blogs | Wptuts+
- Using PHP includes with WordPress — 45royale Inc. — A web design studio in Atlanta, Georgia
- Execute PHP in WordPress post, page and Widget Sidebar
- How to Allow PHP in WordPress Posts and Pages
- 25+ Extremely Useful Tricks for the WordPress Functions File
- WordPress functions.php Snippets | WP FUNCTION ME
- WordPress PHPXref – PHP Cross Reference of WordPress – Yoast
The following resources are for those who develop WordPress Plugins and WordPress Themes and wish to release them to the public and include them in the WordPress official directories, 
Learning from Lorelle 