In this study the "neural efficiency" phenomenon (more efficient brain function in brighter as compared to less intelligent individuals) was investigated regarding differences in intelligence (average vs. above-average intelligence) and scholastic achievement (achievers vs. underachievers). The cortical activation (assessed by event-related desynchronisation in the EEG) of 31 male adolescents was measured while performing a verbal and figural version of Posner's letter matching task and two creativity tasks. During the figural Posner task, average intelligent underachievers showed higher frontal activation than similarly intelligent achievers and brighter underachievers, whereas average intelligent achievers showed higher posterior activation. During one creativity task underachievers were frontally less activated than achievers. The results provide first evidence that different achievement levels are also reflected in different levels of cortical activation. (Contains 3 tables and 3 figures.)