They don't want you to list the same employer twice but in the situation it is *much* better to do that then to give misleading dates.
I feel that it's worth the risk and I imagine they will understand why you needed to list it twice, because of the subsequential gap due to returning to school.
If you would rather leave off the internship then there's a way for you to show this on your resume to emphasize the progression factor. You don't have to fill out three boxes and this might be the best way to handle this situation.
This client gave me permission to share all of his materials out of gratitude for me getting him into Wharton with a 650.
He had a similar situation, internship graduated then full time
DASSAULT FALCON JET 2012, 2014 – Present
Program Engineer, Department of Service Engineering, Little Ferry, NJ 2014 – Present
Create and deliver programs to ensure reliability of 116 private jets located across the Western Hemisphere.
Collaborate with FAA to improve fleet airworthiness; implement jointly-derived solutions and best practices.
Promoted in August 2016 to develop ancillary services for a fleet of 1350 new aircrafts and lead price negotiation
discussions with aircraft part suppliers.
Programs reduced all Western Hemisphere flight cancellations by 35%, including 61% reduction for Asia-based jets
Conducted jet update seminars in 10 cities across North America and Europe; 98% of clients rated presenter as being
clear, concise, and a subject-matter expert.
Prevented grounding of 265 jets by conducting effective negotiations with FAA.
Obtained authorization for $24M in parts; developed multivariate model to determine new part allocation.
Founded Corrosion Prevention Program in 2015. Partnered with 8 service centers throughout Asia, Europe, and the
Americas to implement the program; later rolled out to all updated plane models.
Saved clients $5M in immediate
repair costs and prevented client payout of $380M in corrosion repair costs over the life of the fleet.
Internship – Developed design for aircraft cabin parts. Hired upon graduation. Little Rock, AR 2012
PEUGEOT CITROËN, Internship – Sound-tested newly developed car models, Velizy, France
https://mbaprepcoach.com