There is quite a bit of overlap in abilities of the students. Meaning, the smartest kid at BYU-I probably isn't that different than the smartest kid at BYU. However, there is a higher proportion of kids at BYU-I who struggle academically and would not thrive or survive at BYU.

I went to BYU-I for a year before my mission. This was fall of 2006. Most of my LDS friends went to BYU. I didn't even apply to BYU while I was in high school. My freshman year was more real life than my friends at BYU. I lived off campus in an apartment with a kitchen and made all my own meals, had a job working 30+ hours per week doing construction, had difficult classes, etc. My friends at BYU on the other hand, lived in dorms, ate in a cafeteria and lived like it was a constant party. It was like glorified high school with no parental supervision. IMO, my freshman year at BYU-I was much more useful in preparing me for a mission and life than their freshman year at BYU. Lots of people value and want the freshman experience my friends had at BYU. I value the experience I had and think more people would benefit from a similar experience.