A cross-sectional approach covering an age range of 10 years was used to compare the developmental changes in picture naming and number naming of 77 high school and 74 elementary students who came from Germany to Sweden. For the two different groups of students, length of residence in Sweden was the main independent variable and reaction time on simple naming tasks of pictures and numbers in German and Swedish was the dependent variable. The results provide evidence that elementary school students achieved a balanced form of bilingualism 2 years earlier than high school students on the picture naming task. Naming two-digit numbers was shown to be a relatively difficult task for elementary school children, as indicated by markedly prolonged response times. Despite this fact, after about 4 years of residence in Sweden, both groups of students reached language balance on this task in that they showed identical response times in both languages. The results on the picture naming task were taken as support for the optimal age hypothesis.