Abstract The aim of this study was to investigate how a group of pupils developed in their written language in grade 5. The study proceeds from my hypothesis that a number of textual variables, such as average text length, average sentence length, the average length of the initial clause constituent, and the proportion of long words, ought to rise during a term. The material consists of over 600 texts written by 14 pupils. All the texts are analysed with the LIX tool available on the Internet. The texts are entered into the LIX counter which then returns a value for the studied variables. This procedure was performed for all the variables except initial clause constituent length. That is instead calculated manually by counting the number of words per initial clause constituent. The result shows that all the variables except the proportion of long words increase during the term. The average text length is the variable with the most noticeable increase during the whole term. The proportion of long words, however, did decrease during the same period. The results also show a great correspondence with earlier research on upper secondary pupils’ writings. This means that the group of 11 years old multilingual pupils in this study write with the same proficiency as 16–19 years old pupils, as regards the variables average text length, average sentence length and the average length of the initial clause constituent.