Question: Can doing a post-graduate year improve or decrease chances of admissions to a top tier or Ivy League college?
Doing a Post-Graduate (PG) year will rarely hurt admission odds (unless the GPA goes down or the student gets suspended for bad behavior or lands in similar hot water). The PG year might raise Ivy or elite admission chances but only for those who were reasonably strong candidates to begin with and then used the PG year to prove themselves in additional ways.
Commonly, talented athletes will spend that extra year honing their prowess in a sport in order to catch a coach’s eye. For non-athletes (or even so-so ones) the PG year may not provide that same clout but can sometimes be helpful, too. For instance, students who use it to focus on some academic passion (e.g., scientific research) may find that this additional year makes them stand out at admission decision time. When English is a second language, the PG year can provide a time to raise TOEFL scores and to show that an already outstanding student is also fully fluent in English.
But simply spending an extra year in high school is not likely to boost Ivy or top-tier admission odds unless the student accomplishes something significant during that year that will help set him or her apart from the hyper-competitive crowd.