Students must take six 90-minute written exams over three days in June or September, consisting of common and specific subjects taken in Spanish Baccalaureate or Bachillerato (the last two non-compulsory years of secondary education).
Selectividad or Scholastic Aptitude Test is accepted by USA universities if accompanied by TOEFL English exam.
Now, these exams have two parts: Everybody has to do this part, and it consists in 4 compulsory tests (5 in case of Galicia, Catalonia, Valencia, the Basque Country and Balearic Islands) In this part the students can choose between 2 and 4 subjects (whatever you want depending on your specific "Bachillerato" and the specific weights published by each university) and can obtain a maximum of 4 extra points.
Other subjects, such as Spanish Language and Literature or History of Philosophy consist on a text which requires a writing task about it, theory questions and vocabulary.
In "Matemáticas orientadas a las Ciencias Sociales" (Applied Maths) a table with the standard deviation is given.