The purpose of this paper was to look at children’s vocabulary development in written English from 5th grade to 9th grade. This was investigated by having the students write about the same comic strip. I wanted to explore what some previous research said about second language vocabulary acquisition and then compare these results with my own investigation. Therefore, some of the strategies that enable students to enhance second language vocabulary are also accounted for. The results show that the difference between students in grade five and students in grade nine was not as noticeable as expected. The investigation also revealed that students’ writing was influenced by their first language, in this case the Swedish language. Further, the students used a variety of made-up words and phrases. This might be caused by an insufficient L2 vocabulary at this age (12-16 year olds) for a task such as the one given. It can also be explained by a wish to avoid vocabulary difficulties. Type/token ratio was used in order to see how extensive the vocabulary was in both groups. Students in their ninth year used a vocabulary with more low frequency words than the students in their fifth year. One conclusion that can be drawn is that second language vocabulary acquisition needs to be more focused on students’ initiatives. It can also be concluded that high frequency word training is valuable since these are the words mostly used by students in both ninth and fifth grade of compulsory school. Nyckelord: Vocabulary development, second language acquisition, high and low frequency words, type/token ratio.