The cut-off levels of insufficient literacy skills used in national and international literacy studies have not been validated. Thus, it remains uncertain whether adult poor readers are handicapped by insufficient reading skills in everyday life, i.e. in job-related or educational activities. The primary purpose of the study was to identify a minimum level below which insufficient reading skills proved a handicap to adults in their educational efforts. One hundred and eighty-nine adults in formal adult education participated in the study. The adults' reading comprehension, decoding skills, primary language, level of exam, student and teacher ratings of the adults' reading skills, and the adults' exam grades for courses in formal adult education were obtained. Exam grades below the mean were taken as documentation of educational failure. Adults in the lowest percentile in reading skills only managed to obtain exam grades below the mean in courses placing heavy demands on their reading skills, indicating that poor reading skills were in fact a threat to the adults' educational achievements. Possible causes of insufficient reading skills were further examined. Adults in the lowest 10th percentile suffered from very poor decoding skills. Even though a larger variation was seen in the exam grades for adults in the 10-25th percentile, they too, were handicapped by poor reading comprehension. The decoding skills and socio-economic data of these adults indicated that improved reading skills might increase their chances of getting an education.