Secondary education in Spain varies significantly from the US high school system. After completing Primary Education (first through sixth grade), students go onto four-year Obligatory Secondary Education (ESO). In Spain, education is only obligatory until 16 years of age, when ESO finishes.
After ESO, students have several options if they choose to continue their education. They may continue on one of two tracks: Bachillerato (traditional college prep track, similar to junior and senior years of high school) or Professional Training (Vocational or Art School). In June, when the final year of Bachillerato ends, students take the national university entrance exam and apply to university programs based on the weighted average of their exam results and their GPA for the Bachillerato cycle.
The college application process is much less extensive in Spain since most high-school graduates will seek admission to the public university in their home city or region. It is important to highlight that most Spanish applicants are not accustomed to thinking about where they will attend university until the second half of their senior year. As a result, many Spanish applicants for undergrad studies in the US will find it useful to take a gap year to prepare for the TOEFL and SAT/ACT.