The material in school itself is fairly easy provided that you actually study, meaning: go to every class, ask questions about things you don't get, take notes on things to look up later, and then read the assigned readings and do the assigned homework. The material itself is dumbed down to high school level reading.
What many people find hard are the different paces of different programs. One school near me is 1 year long (with an additional 4 month prep course in anatomy, physiology and pathophysiology), and time is split very evenly between ride time, clinical time and class time.
The school I went to was 8 months in length, no prep course required (although, I had taken one elsewhere and taken good prereqs that weren't required), and then the ride and clinical time was condensed into about 4 of those 8 months, which meant 100+ hour weeks during those 4 months, plus working anywhere in between. The schedule was very prohibitive to sleep, and I got very little sleep for 4 months, and that "very easy" material suddenly became very hard when faced with no sleep. But, I completed school and passed everything on my first try in 8 months. In contrast, some friends of mine went to the "other" program, it took them 16 months in total (all of this excluding EMT school), and many still said they found school to be hard for various other reasons.
Additionally, are you going to school while trying to feed a family of 6, or are you 19 and live at home with mom and dad who are helping you pay for school. Those things greatly effect your performance as well.