Previous studies have shown that where bilinguals have a poorer grasp of some language than monolingual speakers of that language, the deficit has almost invariably revealed itself in reading skill. Also, the deficit in language is usally associated with a relatively lower mean IQ for bilinguals when tested orally. Bilinguals have also been found weaker than monolinguals in problem arithmetic, but not in mechanical arithmetic. The author does not imply that bilingualism is necessarily connected with a language or intellectual deficit; he attempts, rather, to explain such deficits when they occur. In his studies of reading speed and problem solving in English and Irish, carried out with fifth and sixth grade children in Dublin and Dundalk primary schools, significant differences between languages were found in the speed at which subjects interpreted the meaning of individual words and sentences, in the speed at which subjects could pronounce words, and in ability to anticipate the sequence of words in continous prose. The implications concerning these differences for bilingual students are discussed. (AMM)