BACKGROUND: Children who have poor vocabulary knowledge are at risk of wider language weaknesses and reading comprehension difficulties, which will impact upon their educational achievement. The central question addressed in this paper is how best to teach new vocabulary items to these children. AIMS: To investigate the effects of two different methods of teaching vocabulary on both vocabulary knowledge and reading comprehension. Methods & PROCEDURES: Twenty-four children (aged 7-8 years) with poor existing vocabulary knowledge took part in an intervention study. Half the children were taught new vocabulary items using definitions; the other half were taught a strategy for deriving meanings from written context. Tests of vocabulary knowledge were given before teaching, immediately after teaching and 3 months later. OUTCOMES AND RESULTS: Immediately after teaching, both groups had improved equivalently in vocabulary knowledge for the taught words. However, 3 months later, the context group showed significantly better expressive vocabulary knowledge. The context group went on to show significantly better comprehension of text containing a number of the taught words and demonstrated that they could use the newly acquired strategy independently to derive meanings from written context. CONCLUSIONS: The context method developed is effective in increasing vocabulary knowledge and improving reading comprehension in children with poor existing vocabulary knowledge, and this is therefore recommended for use with children who require extra help developing vocabulary and comprehension skills.