What is the difference between a Specialist and a Corporal in the Army? Inquiring Marine minds want to know.

A Corporal is basically an E-4 that has been thrust into a leadership position. I was a Spec4, but found myself in charge of our Communications section when our Sergeant ETS'd. I was later rewarded with my hard stripes for my efforts

Both are pay grade E-4. The Corporal is a Junior NCO and is ususaly in a leadership position, where the specialist is not!

A corporal is considered an NCO, and a specialist is not. Although both have the same paygrade, a corporal would be the specialist supervisor.

a corporal is a junior noncommissioned officer and he or she is put in more leadership positions vs a specialist

In the Army rank structure, a Corporal is a junior non-commissioned officer. A corporal may be assigned as a Team Leader in a Squad. And in some cases he may be the Squad Leader when units are short on NCO's. The Specialist is not a junior non-commissioned officer or in a leadership position.
However, from my time in the 70's, it was not uncommon for a Specialist or even a Private First Class to be assigned as Team Leaders / Squad Leaders. For the most part they did very well on their duties.

A Corporal and a Specialist have the same pay-grade. The theoretical difference is that the Specialist is not in a leadership role while the Corporal is an Non Commissioned Officer (NCO) with all the potential responsibility of a Sergeant but no pay to compensate for said responsibility.
Some units are "good" about putting the Corporal rank on a Specialist that is put in a leadership role, while other units, not so much.

based on what I know of the Marine Corps, and having been a Spec4 and new a few Cpls.... the easiest way to describe it is ALMOST: what is the difference between a Marine SgtMajor and Master Guns? (ok, both are E-9....bear with me here)..... the Cpl would be more similar to the SM, the SPC4 would be more similar to the Master Guns....but instead of being E-9, they are E-4..... it boils down to duty description and responsibilities....Leader of troops or mentor/worker. Now, I also know that a Master Gun can break into some ass if needed...so this is all quite a stretch.... ;-)

SGT Dave Tracy... Sorry, but you don't have the full picture. Let me fill you in on the Marine view.
Specialist ranks are just that. They specialize in something... and that is their job, which, I am sure they do well to the best of their abilities, and you have my full respect for that.

Now, a Corporal in the Marines is a different thing. First and foremost, they are considered a leader of troops when necessary. I've seen Cpls doing most everything from leading troops, stepping in for section leaders, running working parties and putting boots thru Parris Island.

Perhaps, its different in the Army, but in the Marines, you get that second stripe, you are EXPECTED to lead. We used to joke among ourselves, that being a CPL was more like a SGT with training wheels... you still got crappy details at times, but the difference was that more often than not, YOU were in charge of the crappy details instead of actually DOING said detail. Then again, perhaps it was just my experience and others have a different view.

The specialist ranks (they once ranged the whole of the pay grades from E-4 and up) grew out of the Tech Sergeant ranks of WWII.

The Army wished to differentiate between the NonCommissiined Officers who led soldiers and those soldiers who had technical or other skills to provide the Army, but had no rhyme or reason to have leadership roles. For example, an Army Sergeant First Class would be a platoon sergeant, while a Specialist 7 had pay and privileges of a Sergeant First Class, but did not have leadership duties or training in command and leadership.

The Army phased each of the higher Specialist ranks out, but retained the Specialist 4 (now just called Specialist, except when referring to the Spec 4 mafia). Corporals are non commissioned officers. Specialist are not. However, many a Specialist is in a leadership position nowadays (team, and occasionally, even squad leaders), so what the reasons that remain for retaining the dual ranks is unclear, other than like most things military related, doing things that make sense is against the good order and conduct of military operations.

A CPL is a unit promotion and will not follow the Soldier to the next duty station. It is basically a rank if a unit does not have enough NCOs and need some for supervision/other duties.