I go to a DO school with a tiny class size, so we know exactly who the first and second year rockstars are. One kid in particular exemplifies most of the top 10 or so at my school (with a few exceptions):
1. Consistently nailed 90+ on some pretty ridiculous immuno, micro, path, and biochem/genetics exams taught by some pretty intense phd's or md/phd's at our school (people that had mostly only taught phd students in their past lives).
2. Homeboy lives about two miles away from school (with mom and dad)
3. Spends most every non-academic moment "gaming"
4. Cracked >250 on the USMLE
5. Is clueless on the wards. CLUELESS. Gets shredded on a daily basis by attendings that don't know "who" he is when presenting patients. He's the classic example of someone that works really hard over the course of the first two years, blows off simulated patients, rocks the boards, and then goes on a mental health break during the clinical years.
In his defense, I will say he has some schizoid personality features and a few ticks here and there that don't really help the situation. He's shooting for rads.
Based on my observations, the more average students tend to really step up their game during 3rd and 4th year. Given that they're average rather than poor students, and their basic sciences foundation is solid, they tend to shine at the end of the day.