My student reluctantly passed the transcript across the table to me. "I don't know what happened in my sophomore year," he said. "I guess I screwed up."

I tried to reassure him as I calculated his GPA. However, despite my efforts, the numbers were clear: He would not be eligible for the more selective of California's public university system, the University of California.

After my student went home, I pulled out my calculator again and crunched the numbers. It didn't take long for me to see that he was close to eligibility for the UC, but not close enough. There are several paths to admission, but this student did not meet the criteria for any of them. He had taken all the right classes and been the captain of his lacrosse team. His test scores were fine, but his GPA just didn't add up. Despite a few scattered A's and B's in his freshman and junior years, his sophomore year sealed his fate.

The University of California doesn't use freshman grades when determining GPA, so with five C's in his sophomore year, my student had closed the door to one of the most prestigious, respected and affordable university systems in the country. He was several tenths of a point away from eligibility.

In its most recent State of College Admission Report, the National Association for College Admission Counseling (NACAC) says that the four most important factors used by colleges when making admission decisions are, in order of priority, grades in college prep classes, strength of curriculum, admission test scores and overall grades in all courses.

While the private colleges have a tendency to also look at factors other than grades, the public colleges seem to care a great deal about grades, and many have minimum GPA's for admission. Nevertheless, the NACAC survey demonstrates that all colleges scrutinize grades in individual classes as well as the overall GPA.

There is a misconception that in college admission, the junior year grades are the most important. Colleges look at an overall average GPA from either sophomore and junior years or all of high school. Some also look at first semester grades from senior year. Junior year grades are important because that is when many students take their most challenging courses, but those grades don't necessarily have more weight than the grades from other years. Colleges will be mindful of upward trends in grades, but a dismally low GPA is hard to overcome.

Freshmen and sophomores need to know that grades are very important. Slacking in a class, not studying for a test, debating whether to complete an extra-credit assignment or turning in a term paper late could be serious mistakes. Moreover, even with straight A's for an entire year, statistically, it's tough to resurrect a hopelessly sagging GPA.