Sixth-graders? ability to understand textbook vocabulary

My previous study aimed to find out how well primary school pupils are, after six school years, able to derive the meaning of an unknown word from written context when reading a non-fiction text. For this purpose, 158 sixth-graders read a newspaper article about a shipwreck found at the bottom of the Baltic Sea. After reading the text, the pupils were asked to explain what ten words underlined in the text meant in this particular text. The results showed that several pupils had great difficulties in the task. One third of them explained less than half of the words correctly. Only 8% of them explained all the words correctly and 5% of them could not explain any of them. Still today, the textbooks are for the pupils an important source of new information. Therefore, it was necessary to explore if the vocabulary used in these books contains words that they do not understand. In addition, the aim was to find out if the pupils have learned to derive the meanings of unknown words from the text context. Altogether, 247 sixth-graders took part in the study. About half of them read a chapter about whales in their natural science book and the other half a chapter about Great wall in China in their history book. After that the pupils explained the meanings of ten words underlined in the text. The results show that both textbook chapters contained words that were unfamiliar to many pupils. In the history book group, one third of the pupils explained less than half of the words correctly. Only 2% of them explained all words correctly and 4% of them could not explain any of them. Although the words in the natural science book seemed to be easier to explain, many pupils had difficulties in understanding them too. In the natural science book group, 22% of the pupils explained less than half of the words correctly. Only 3% of the pupils explained all words correctly and 2% of the pupils could not explain any of them.When comparing the results with the results of the previous study, it is obvious that for the sixth-graders the text in their textbooks is almost equally difficult to understand than newspaper articles. If the text includes several words that remain incomprehensible to the reader, it is possible that the comprehension of the text and acquiring new information from it is impossible.