What will infantry school be like as a prior service SGT from the marines that already has a combat deployment under their belt goin army ?

Be humble and let your skills, knowledge, and expereince speak for them selves. Your value will show through your work and discipline. The Marine Corps is a great institution and you will see that the things you learned in the USMC will be a great help in being a good soldier. Let your actions, initiative, enthusiasm, compassion, politeness, physical fitness, wisdom, and attention to detail speak for itself. Best wishes, Larry Dandridge

It depends on your outlook, your attitude, and your ability to be a good teammate. You will not be treated like "some Dude" because the Drill Sgt.s will know your background. You will probably be a Squad Leader. They will hold you to somewhat a higher standard. During my decades of service I've spent time around Marines, and did some time at Camp LeJeune. I've never been treated like a piece of $hit. I was a Buck Sgt. at the time. I wasn't disrespectful, nothing, the mess Gunny reminded me of Sgt. Carter on Gomer Pyle USMC. You may be disappointed by the lack of respect, the lack of esprit de corpse, and discipline. The Army used to be somewhere between where the Marines are and where the Army is today. I say to check any Marine "arrogance" at the door. Nobody will care that you were a Marine, and they will come back at you, "apparently you couldn't handle it," or, "if you loved it so much, what are you doing here?" Also, don't do a bunch of, "when I was a Marine we..." Well, you aren't a Marine any more, so who cares. I'm not saying it derogatorily to you, but that's what will be said and the attitude. Nobody's going to fall at your feet and worship you, they're not going to kiss your butt, and they are going to expect a little more out of you.

Why do you need to go to Infantry training?
Are you switching jobs?
If you're 0311, you just switch uniforms and show up. If not, you just go through the MOS portion of OSUT, if anything at all.

Dont be a dirtbag and you wont get treated like a dirtbag. Remember that no matter how your treated the trainees will look to you too so set the example. Bad habits like carrying your M4 by the slip ring, not using two hands or no hands to get up and down, basically just do what your told how your told and maybe just maybe the Drill will appreciate it and give you some slack. No guarantees.

Having a combat deployment is pretty much irrelevant. When I went Army, I had to do Basic Training because even though I had a Nam tour with the USMC infantry (Corpsman), I was Navy and Navy or USAF had to do Army Basic. At that time (1971), prior service Army or Marines did NOT have to do Army Basic unless they were out for a specified time period. In your case, that's not an issue. You PROBABLY won't have to do Army Basic. Speak to an Army Recruiter, even though they haven't given you an answer, for the latest policies and diplomatically push for a solid answer or ask to speak to the Recruiting Office's NCOIC.

There are some protocol differences in the Army ... like when formally reporting to an officer, Army DOES salute whereas Marines and Navy do not salute indoors.

As for "Infantry School," I'm not entirely sure; but it's likely your USMC Basic will suffice. I don't THINK you'll have to do Ft. Benning's Infantry Basic. If you're going Rangers, that's different and you'll have to pre-test for that anyhow.

First, good luck! Second, I too was an active-duty Marine that actually got out and then went into the Army 10 years later. Not sure why you are going through infantry school unless you were not infantry in the Marine Corps. I was an 0311, kept my rank with time and grade (even after 10 years) and did not have to attend 11B or PLDC (I had already attended MC NCO Academy). I signed on the dotted line and was awarded 11B and signed up for BNOC as soon as I arrived at my unit. I was told all of my schools attended while in the Marine Corps would far exceed what was required in the Army. If you are not currently MC Infantry, then it makes sense if you want the MOS. Hold on, buckle up, do as your told and enjoy Sand Hill!

Frankly, a lot of it may come as something of a letdown. Just keep in mind that Marines and Army do some stuff the same and some stuff differently, so be flexible.

As a marine if you don’t have 5 years break in service you be an insert: skip basic and join AIT class.
For more info check this link; https://m.goarmy.com/careers-and-jobs/current-and-prior-service/continue-serving/transitioning-services/inter-service-transfer-program.m.html

During training,you should be treated as a permanent party and not as IET.
TRADOC Regulation 350-6
4-15. Reclassified/MOS trained/prior service Soldiers
a. Reclassified/MOS trained and prior service Soldiers are those individuals, in any grade, who have previously completed IET and are attending skill level 1 training in IET units as a result of reclassification or enlistment actions. Reclassified and prior service Soldiers are not considered IET Soldiers; however, they are assigned to IET units. This definition does not apply to those Soldiers who failed to complete the requirements for the award of a MOS as part of the initial IET process. Reclassified and prior service Soldiers must meet all course requirements for graduation (APFT, etc.), unless otherwise stipulated in this regulation.
b. Reclassification policy, see AR 350-1 for reclassification requirements.
(1) Prior service personnel entering the Active Army are not required to attend BCT if they completed Army or U.S. Marine Corps basic training, or completed training for U.S. Air Force or U.S. Navy Special Operations Forces, or U.S. Air Force Security Police, and have less than a 3- year break in service.
(2) Prior service personnel entering the AC will attend Army BCT if they have not completed Army or U.S. Marine Corps basic training, or completed training for U.S. Air Force or
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U.S. Navy Special Operations Forces, or U.S. Air Force Security Police, and have more than a 3- year break in service.
(3) Prior service personnel are not considered IET Soldiers but will comply with applicable regulations, standards, and training requirements.
(4) Prior service personnel who enlist for an MOS held during their previous enlistment and have less than a 3-year break in service are assigned directly to operational units.
(5) Prior service personnel who enlist for a MOS not previously held, and have less than a 3 year break in service will attend AIT in the new MOS. If the new MOS is taught in the OSUT mode, the individual Soldier will enter training at a point in training where the AIT portion of the instruction starts and continue until all MOS training is accomplished.
c. Treatment.
(1) Prior service personnel in the pay grade of private (E-1) through specialist (E-4) should be offered non-IET barracks if available and feasible. If not, they may be billeted with the general IET population.
(2) Prior service personnel in the pay grade of sergeant (E-5) through sergeant major (E-9) are billeted separately from other IET Soldiers. Prior service NCOs are billeted in a separate building when possible. If a separate building is not available, then on a different floor of an IET barracks. If a different floor within the building is not possible, then within a separate room (not in an open bay). Prior service NCOs may be billeted with IET Soldiers as a last resort with approval of the USACIMT. Requests should be submitted in memorandum format. Billeting NCOs with IET Soldiers is not the intent and should be a last resort.
(3) The billeting of prior service NCOs also applies to RECBNs. RECBNs will immediately identify prior service personnel and ensure the gaining BCT/OSUT units are informed of the prior service personnel’s status, rank, pay grade, and billeting standards. If necessary, prior service BCT/OSUT NCOs may be housed in AIT facilities.
(4) Privileges for reclassified and prior service personnel.
(a) Although reclassified Soldiers are subject to IET policies and procedures, their privileges should be the same as those of permanent party members of equal grade. They are treated with the dignity and respect due their grade.
(b) The company commander determines specific privileges based on such factors as grade, training performance, self-discipline, motivation, and conduct.
(c) Fraternization between reclassified, prior service Soldiers, IET Soldiers, and cadre is forbidden in accordance with AR 600-20.
d. Duties/responsibilities.
TRADOC Regulation 350-6
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TRADOC Regulation 350-6
(1) Commanders may take advantage of the experience and leadership abilities of reclassified and prior service Soldiers, and use them to augment their cadre. However, the primary duty of reclassified and prior service Soldiers is to attend training and become technically proficient in their new MOS.
(2) Prior service NCOs in training may assist with IET Soldiers with regular cadre oversight after appropriate orientation and certification by the company commander/1SG on TRADOC policy regarding leadership and treatment of IET Soldiers.
(3) AIT/OSUT commanders will evaluate each prior service Soldier's proficiency in all areas (not just MOS subjects) and ensure training is provided, as required. Use reclassified and prior service Soldiers who are proficient in common tasks as demonstrators and assistant instructors.
(4) Commanders are encouraged to integrate reclassified and prior service personnel with IET Soldiers during training to enhance training by taking advantage of their knowledge, experience, and leadership abilities.
e. This paragraph is not applicable to individual ready reserve (IRR) Soldiers reactivated to military service. Appendix J, the IRR mobilization (MOB) training strategy.

You will be separated from E4s and below.
You will keep your cellphone on you.
Rule of thumb ,you need to show respect to the Drill sergeants,your fellow trainees ; as a matter of fact everyone because respect is reciprocal.Shut up,listen,and don’t try to run the show own your own,just do your best but in a low key manner.

Infantry training is tough, challenging and exhausting no matter whether you are army or marines. As a Vet you will know the routine, so help out, blend in, and when necessary display leadership and expertise. Don’t brag about “how’s it done” or marines do it this way. Just do it.

First, thank you for your continued service. Your prior military experience is valuable and it will assist you, more importantly you can emerge as a mentor to the ones that will struggle. I will personally not state your prior service with the marines until the last day, you don't need to and the truth nothing good will come from it, all you will be doing is placing a unnecessary target on you.