The aim of the article is to portray problems a bilingual child can experience during simultaneous acquiring two tongues and to help teachers to overcome these problems and to raise the linguistic efficiency of the bilingual child. In the article linguistic mistakes made by the fourteen-year-old boy living in Australia were presented. Analysis of his linguistic mistakes and conclusions about the linguistic level with reference to the Polish language, in the ability of building correct sentences under the lexical and grammatical account, allowed to show concrete actions a reader may and should take in order to raise the linguistic level of boy in the second tongue.