SA Background Check???

Hi all,

To keep a long story short, I was terminated from a paid internship at a local accounting firm that I had in high school. The termination in my opinion was not just (was told I worked too slow despite 2 years of no complaints from any supervisors), but I decided to leave it off my resume regardless. Flash forward two years later and i'm applying for some Summer Analyst positions. Obviously these jobs come with background checks to verify employment. My question is: will a background check reveal this left off job? If so will they question it or try to contact the firm? Thanks in advanced, I appreciate any insight.