Instead, education systems that contain a large proportion of selective schools lend to have greater variation in performance between schools (OECD 2010). However, it is reasonably safe to assume that in countries such as Serbia, which still lag behind in tertiary enrolment, the tertiary system might be under pressure to expand and absorb (increasing numbers) of candidates." Upward trends in tertiary enrolment would indicate the same (indicators AE.6).