There is not a '... difference between how cadets at civilian ROTC and SMC are offered active duty ...' with the exception of those below the AD line at an SMC with PMS recommendation. It is based on your performance academically, physically, and as a leader.
AROTC Parent's comments are mostly on point. At an SMC, Army ROTC Cadets must in addition to being recommended by the PMS, successfully complete the ROTC Program and be medically and physically qualified for active duty. The successful completion and rcommendation of the PMS are key and in practice cadets are measured against the other cadets in the Cadet Command - especially for branch selection. Those at SMCs who don't make it, however, are relatively few as cadets self select during their four years. At SMCs unlike at civilian schools with ROTC Programs, all Cadets are required to remain in ROTC and typically the Army ROTC Program is the default program - even though they have no intention of commissioning. Today less than half of SMC graduates enter the military as there are too many other opportunities. So there is the great possibility there are juniors and seniors on the cusp who decide late they do want a contract and frankly are not qualified. They typically are the ones who do not receive a recommendation from the PMS. Technically, at an SMC, those in the Army Program who meet the minimum academic requirements and receive the recommendation of their PMS at SMCs, are required by law to be offered active duty. In practice, the process of selection is similar to those in civilian school ROTC Programs, and cadets pretty much know by their Senior year if they are going to be selected.
Below is the US Code of Laws provision providing for active duty if recommended by the PMS:
10 USC 2111(a) Support for ROTC
(e)Assignment to Active Duty.—
(1)
The Secretary of the Army shall ensure that a graduate of a senior military college who desires to serve as a commissioned officer on active duty upon graduation from the college, who is medically and physically qualified for active duty, and who is recommended for such duty by the professor of military science at the college, shall be assigned to active duty.
(2)
Nothing in this section shall be construed to prohibit the Secretary of the Army from requiring a member of the program who graduates from a senior military college to serve on active duty.
(f)Senior Military Colleges.—The senior military colleges are the following:
(1)
Texas A&M University.
(2)
Norwich University.
(3)
The Virginia Military Institute.
(4)
The Citadel.
(5)
Virginia Polytechnic Institute and State University.
(6)
The University of North Georgia.
(e)Assignment to Active Duty.—
Pub. L. 104–106, div. A, title V, § 545(a), Feb. 10, 1996,
110 Stat. 317; amended
Pub. L. 105–85, div. A, title V, § 544(d)–(f)(1), Nov. 18, 1997,
111 Stat. 1745, 1746;
Pub. L. 106–65, div. A, title V, § 541(c), Oct. 5, 1999,
113 Stat. 607;
Pub. L. 113–66, div. A, title V, § 583, Dec. 26, 2013,
127 Stat. 776.)