This paper deals with issues of assessment of various levels of textbook.
As a starting point we used the works of three authors: K. Nestlerova, J. Průcha and M. Pluskal.
First we characterised and examined an overall level of difficulty together with syn-thetic difficulties and problems with concepts in didactic texts.
We also considered further parameters of assessment such as approx. length of the sentences, coefficient of density of special information and coefficient of general in-formation.
The subjects of the research were chemistry textbooks for upper-secondary schools, and conclusions were based on the results of a questionnaire survey carried out in 57 gymnasiums‘ (academic high schools) with the highest academic profile in Czech Republic and a survey of the range of chemistry text-books available on the book market. There were 6 textbooks mainly used by schools.
The results of the survey showed that the textbooks could be classified in terms of difficulty.
In the case of the textbooks for upper-secondary schools mentioned above, three levels of difficulty were identified - from easier to intermediate up to advanced.
None of textbooks can be described as elementary or extremely difficult. This fact enables teachers to adjust teaching level in line with different school frameworks of education. The method described in this work could serve as an inspiration for the design, assessment and finally the selection of suitable textbooks.