I'm learning in my college class that World War I was really fought because Britain wanted to block Germany from accessing oil in the Middle East.

Oh God. No. Why!??!

But seriously, that's insane.

World War I was not about oil. Oil had become a strategic resource for Britain in the lead up to WWI because of the decision to convert the British navy to oil. The vast majority of that oil came from Persia as a result of the British government ownership in the Anglo-Persian Oil Company (later British Petroleum, today BP).

The German navy continued to run on much more easily accessible and abundant coal and did not produce an all-oil ship until after the war.

In other words, there was no immediate need for Britain to "block" German access to a resource that the Germans weren't going to use.

Moreover, oil in Ottoman Mesopotamia, today's Iraq, was at this point entirely hypothetical. There was a pretty good idea that there was likely to be some oil up around Mosul (as indeed there was), but, for instance, the existence of massive oil fields in southern Iraq and Kuwait was not then in consideration.

which would have won them the very economic prosperity that Britain was afraid of.

There certainly was plenty of rail construction going on in the Middle East at the time, which presumably was profitable for the individuals involved. However I have never come across any suggestion that the Berlin-Baghdad railway would have delivered to Germany some greater degree of economic prosperity on a geostrategic scale. That the completion of the Berlin-Baghdad and Hejaz railways might have led to improvements in movement and communications for the Ottomans strikes me as the more important issue.

That the German control of the railway was causing some degree of great power tension between Germany and Britain I think is credible, but no more so I think than French or Russian entry into the Middle East along similar lines.

It's also worth noting that when the war broke out, the Ottoman empire initially remained neutral, and there was hope on the British side that they might either remain neutral or join the with the entente. Had they done so the entire war in Europe would have been fought without any reference to oil whatsoever.

For a real discussion of how and why WWI broke out, see Christopher Clark's The Sleepwalkers, which to my memory doesn't once mention oil. For the Ottoman entry into the war see either Eugene Rogan's The Fall of the Ottomans or perhaps better Sean McMeekin's Ottoman Endgame, which touches on how and when oil came to be seen as being more pivotal to the conflict (namely, at the very beginning when the British secured the Persian Gulf ports when they landed at Basra, and at the very end.)