Question:  “I am a recent graduate with my Masters in Occupational Therapy.    One of our professors recommended that we keep our resume/CV to one page.   In my case though, I worked for 3 years as a Behavioral Interventionist with children with autism before I started grad school.   
In addition, I have several excellent externships/clinicals during my Masters that I would like to mention.   
Should I include my pre-masters experience, or ditch it and stay with the single page?”
Answer:  The one page resume convention, is just that – a rule of thumb, and is not something that should be set in stone.   If you have experience that pre-dates your degree and is highly relevant to your career path  – and in your case it IS – by all means include it in your resume and go to two pages.    But still be stingy with your word count!