The main topic of this paper is reading comprehension. The paper offers an overview of reading development and reader's skills from the earliest beginnings of print awareness until the pinnacle of reading skill that is reading comprehension. The paper describes in detail what exactly reading comprehension is and why it requires automaticity and the ability to connect knowledge about the world with what has been read. Emphasis is put on non-literary texts because they are the least represented types of texts in school. Furthermore, children most often encounter exactly those types of texts in their free time, and they are incredibly important because they contain fundamental information and knowledge that affect personal life. Thus, a non-literary text was selected for this research. The text teaches about the functions and importance of the brain and how to train it to improve long-term memory. A research was conducted on that text with the purpose of checking reading comprehension in fourth graders. In total, 80 students from 2 primary schools (7 fourth grade classes) participated in the study. The first part of the questionnaire contained questions for which students had to write answers on their own, while in the second part they needed to complete the sentences. Before starting, an instruction was given that all the answers could be found within the text. In spite of given instructions, the result of the first part of the questionnaire has shown that non-literary texts truly do cause comprehension problems. The most highly corroborated and important conclusion of the research is a confirmation that students with siblings have a better developed reading comprehension than students who are the only child in their family. Therefore, family environment surely affects reading development.